Processor capable of executing packed shift operations

ABSTRACT

An apparatus for performing a shift operation on a packed data element having multiple values. The apparatus having multiple muxes, each of the multiple muxes having a first input, a second input, a select input and an output. Each of the multiple bits that represent a shifted packed intermediate result on a first bus is coupled to the corresponding first input. Each of the multiple bits representing a replacement bit for one of the multiple values is coupled to a corresponding second input. Each of the multiple bits driven by a correction circuit is coupled to a corresponding select input. Each output corresponds to a bit of a shifted packed result.

RELATED APPLICATIONS

[0001] This is a continuation-in-part of application Ser. No. 08/610,495 filed Mar. 4, 1996; which is a continuation-in-part of application Ser. No. 08/349,730 filed Dec. 1, 1994, now abandoned.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] In particular, the present invention describes an apparatus for performing arithmetic and logical operations using a single control signal to manipulate multiple data elements. The present invention allows execution of shift operations on packed data types and also allows execution of alignment operations.

[0004] 2. Description of Related Art

[0005] Today, most personal computer systems operate with one instruction to produce one result. Performance increases are achieved by increasing execution speed of instructions and the processor instruction complexity; known as Complex Instruction Set Computer (CISC). Such processors as the Intel 80286™ microprocessor, available from Intel Corp. of Santa Clara, Calif., belong to the CISC category of processor.

[0006] Previous computer system architecture has been optimized to take advantage of the CISC concept. Such systems typically have data buses thirty-two bits wide. However, applications targeted at computer supported cooperation (CSC—the integration of teleconferencing with mixed media data manipulation), 2D/3D graphics, image processing, video compression/decompression, recognition algorithms and audio manipulation increase the need for improved performance. But, increasing the execution speed and complexity of instructions is only one solution.

[0007] One common aspect of these applications is that they often manipulate large amounts of data where only a few bits are important. That is, data whose relevant bits are represented in much fewer bits than the size of the data bus. For example, processors execute many operations on eight bit and sixteen bit data (e.g., pixel color components in a video image) but have much wider data busses and registers. Thus, a processor having a thirty-two bit data bus and registers, and executing one of these algorithms, can waste up to seventy-five percent of its data processing, carrying and storage capacity because only the first eight bits of data are important.

[0008] As such, what is desired is a processor that increases performance by more efficiently using the difference between the number of bits required to represent the data to be manipulated and the actual data carrying and storage capacity of the processor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings.

[0010]FIG. 1 illustrates an embodiment of a computer system using the apparatus of the present invention.

[0011]FIG. 2a illustrates one embodiment of a processor of the present invention.

[0012]FIG. 2b illustrates an alternative embodiment of a processor of the present invention.

[0013]FIG. 3 a is a flow diagram illustrating one embodiment of a process to manipulate data in a register file.

[0014]FIG. 3b is a flow diagram illustrating an alternative embodiment of a process to manipulate data in a register file.

[0015]FIG. 3c is a flow diagram illustrating one embodiment of a process to enable software to manipulate data in a register file.

[0016]FIG. 4a illustrates memory data types.

[0017]FIG. 4b, FIG. 4c and FIG. 4d illustrate one embodiment of in-register integer data representations.

[0018]FIG. 5a illustrates one embodiment of packed data-types.

[0019]FIG. 5b illustrates an alternative embodiment of packed data-types.

[0020]FIG. 5c, FIG. 5d and FIG. 5e illustrate one embodiment of in-register packed data representations.

[0021]FIG. 5f illustrates one embodiment of in-register packed quadword representations.

[0022]FIG. 6a illustrates one embodiment of a control signal format that may be used in the computer system to initiate an operation on packed data.

[0023]FIG. 6b, FIG. 6c, FIG. 6d and FIG. 6e illustrate alternative embodiments of a control signal format that may be used in the computer system to initiate an operation on packed data.

[0024]FIG. 7a illustrates one embodiment of a process for performing a shift operation on packed data.

[0025]FIG. 7b illustrates an alternative embodiment of a process for performing a shift operation on packed data.

[0026]FIG. 8 illustrates one embodiment of a Packed Shift circuit.

[0027]FIG. 9 illustrates another embodiment of a Packed Shift circuit.

[0028]FIG. 10 illustrates an embodiment of a portion of the logic to identify which bits of the barrel shifted result should be corrected (Fixshift).

[0029]FIG. 11 illustrates an embodiment of a barrel shifter.

[0030]FIG. 12 illustrates an embodiment of a multiplexer for a barrel shifter.

[0031]FIG. 13 illustrates another embodiment of a method of performing a packed shift operation.

[0032]FIG. 14a illustrates an alternative embodiment of a Packed Shift circuit.

[0033]FIG. 14b illustrates another alternative embodiment of a Packed Shift circuit.

[0034]FIG. 15 illustrates one embodiment of a circuit for allowing byte alignment with a Packed Shift circuit.

[0035]FIG. 16 illustrates an alternative embodiment of a Packed Shift circuit which allows for alignment shift operations on packed data.

DETAILED DESCRIPTION

[0036] A processor having shift operations that operate on multiple data elements, packed into a packed data type, is described, the processor including an apparatus for shifting packed data. The apparatus has a first shifter configured to perform a shift operation on a first packed data having multiple packed data elements by a shift count to produce a second packed data. The apparatus also includes a correction circuit to produce a shifted packed result, the shifted packed result produced at least partially from the second packed data. The processor allows both for shifting and for aligning of packed data elements.

[0037] In the following description, numerous specific details are set forth such as circuits, etc., in order to provide a thorough understanding of the present invention. In other instances, well-known structures and techniques have not been shown in detail in order not to unnecessarily obscure the present invention.

[0038] DEFINITIONS

[0039] To provide a foundation for understanding the description of the embodiments of the present invention, the following definitions are provided.

[0040] Bit X through Bit Y:

[0041] defines a subfield of binary number. For example, bit six through bit zero of the byte 00111010₂ (shown in base two) represent the subfield 111010₂. The ‘₂’ following a binary number indicates base 2. Therefore, 1000₂ equals 8₁₀, while F₁₆ equals 15₁₀.

[0042] R_(x):

[0043] is a register.

[0044] XR_(x):

[0045] is a register. A register is any device capable of storing and providing data. Further functionality of a register is described below. A register is not necessarily part of the processor's package.

[0046] DEST:

[0047] is a data address.

[0048] SRC1:

[0049] is a data address.

[0050] SRC2:

[0051] is a data address.

[0052] Result:

[0053] is the data to be stored in the register addressed by DEST.

[0054] Source1:

[0055] is the data stored in the register addressed by SRC1.

[0056] Source2:

[0057] is the data stored in the register addressed by SRC2.

[0058] Computer System

[0059] Referring to FIG. 1, a computer system upon which an embodiment of the present invention can be implemented is shown as computer system 100. Computer system 100 comprises a bus 101, or other communications hardware and software, for communicating information, and a processor 109 coupled with bus 101 for processing information. Computer system 100 further comprises a random access memory (RAM) or other dynamic storage device (referred to as main memory 104), coupled to bus 101 for storing information and instructions to be executed by processor 109. Main memory 104 also may be used for storing temporary variables or other intermediate information during execution of instructions by processor 109. Computer system 100 also comprises a read only memory (ROM) 106, and/or other static storage device, coupled to bus 101 for storing static information and instructions for processor 109. Data storage device 107 is coupled to bus 101 for storing information and instructions. Memory includes any data storage medium, such as main memory 104, cache memory, registers, ROM, and other static storage devices.

[0060] Furthermore, a data storage device 107, such as a magnetic disk or optical disk, and its corresponding disk drive, can be coupled to computer system 100. Computer system 100 can also be coupled via bus 101 to a display device 121 for displaying information to a computer user. Display device 121 can include a frame buffer, specialized graphics rendering devices, a cathode ray tube (CRT), and/or a flat panel display. An alphanumeric input device 122, including alphanumeric and other keys, is typically coupled to bus 101 for communicating information and command selections to processor 109. Another type of user input device is cursor control 123, such as a mouse, a trackball, a pen, a touch screen, or cursor direction keys for communicating direction information and command selections to processor 109, and for controlling cursor movement on display device 121. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), which allows the device to specify positions in a plane. However, this invention should not be limited to input devices with only two degrees of freedom.

[0061] Another device which may be coupled to bus 101 is a hard copy device 124 which may be used for printing instructions, data, or other information on a medium such as paper, film, or similar types of media. Additionally, computer system 100 can be coupled to a device for sound recording, and/or playback 125, such as an audio digitizer coupled to a microphone for recording information. Further, the device may include a speaker which is coupled to a digital to analog (D/A) converter for playing back the digitized sounds.

[0062] Also, computer system 100 can be a terminal in a computer network (e.g., a LAN). Computer system 100 would then be a computer subsystem of a computer system including a number of networked devices. Computer system 100 optionally includes video digitizing device 126. Video digitizing device 126 can be used to capture video images that can be transmitted to others on the computer network.

[0063] Computer system 100 is useful for supporting computer supported cooperation (CSC—the integration of teleconferencing with mixed media data manipulation), 2D/3D graphics, image processing, video compression/decompression, recognition algorithms and audio manipulation.

[0064] Processor

[0065]FIG. 2a illustrates a detailed diagram of processor 109. Processor 109 can be implemented on one or more substrates using any of a number of process technologies, such as, BiCMOS, CMOS, and NMOS.

[0066] Processor 109 comprises a decoder 202 for decoding control signals and data used by processor 109. Data can then be stored in register file 204 via internal bus 205. As a matter of clarity, the registers of an embodiment should not be limited in meaning to a particular type of circuit. Rather, a register of an embodiment need only be capable of storing and providing data, and performing the functions described herein.

[0067] Depending on the type of data, the data may be stored in integer registers 201, registers 209, status registers 208, or instruction pointer register 211. Other registers can be included in the register file 204, for example, floating point registers. In one embodiment, integer registers 201 store thirty-two bit integer data. In one embodiment, registers 209 contains eight registers, R₀ 212 a through R₇ 212 h and each register is sixty-four bits in length. R₀ 212 a, R₁ 212 b and R₂ 212 c are examples of individual registers in registers 209. Thirty-two bits of a register in registers 209 can be moved into an integer register in integer registers 201. Similarly, a value in an integer register can be moved into thirty-two bits of a register in registers 209.

[0068] Status registers 208 indicate the status of processor 109. Instruction pointer register 211 stores the address of the next instruction to be executed. Integer registers 201, registers 209, status registers 208, and instruction pointer register 211 all connect to internal bus 205. Any additional registers would also connect to the internal bus 205.

[0069] In another embodiment, some of these registers can be used for two different types of data. For example, registers 209 and integer registers 201 can be combined where each register can store either integer data or packed data. In another embodiment, registers 209 can be used as floating point registers. In this embodiment, packed data can be stored in registers 209 or floating point data. In one embodiment, the combined registers are sixty-four bits in length and integers are represented as sixty-four bits. In this embodiment, in storing packed data and integer data, the registers do not need to differentiate between the two data types.

[0070] Functional unit 203 performs the operations carried out by processor 109. Such operations may include shifts, addition, subtraction and multiplication, etc. Functional unit 203 connects to internal bus 205. Cache 206 is an optional element of processor 109 and can be used to cache data and/or control signals from, for example, main memory 104. Cache 206 is connected to decoder 202, and is connected to receive control signal 207.

[0071]FIG. 2b illustrates an alternative embodiment of processor 109. Processor 109 comprises an extended register file 214. Data can be stored in extended register file 214 via internal bus 205. Depending on the type of data, the data may be stored in integer registers 201, registers 209, extension registers 210, status registers 208, or instruction pointer register 211. In one embodiment, extension registers 210 contains eight registers, XR₀ 213 a through XR₇ 213 h and each register in extension registers 210 is one hundred and twenty-eight bits in length. XR₀ 213 a, XR₁ 213 b and XR₂ 213 c are examples of individual registers in extension registers 210. Sixty-four bits of a register in registers 209 can be moved into sixty-four bits of a register in extension registers 210. Similarly, sixty-four bits of a register in extension registers 210 can be moved into a register in registers 209.

[0072] In one embodiment, extension registers 210 and registers 209 can store either packed integer data or floating point data. In another embodiment, extension registers 210 can be used to store packed floating point data. In this embodiment, packed integer data can be stored in extension registers 210 or packed floating point data. In one embodiment, all of the registers have internal representations that are sixty-four bits in length, the extension registers 210 comprise two internal registers, and integers are represented as sixty-four bits. In this embodiment, in storing packed data and integer data, the registers do not need to differentiate between the two data types. In another embodiment, all of the registers have internal representations that are one hundred and twenty-eight bits in length, the registers 209 comprise half of an internal register, and scalar integers are represented as one of four packed elements each having thirty-two bits.

[0073] Functional unit 203 performs the operations carried out by processor 109. Such operations may include shifts, addition, subtraction and multiplication, etc. but may also include packed shifts and alignment shifts of one hundred twenty-eight bit packed data or of sixty-four bit packed data. Cache 206 is connected to decoder 202, and is connected to receive control signal 207. Control signal 207 may also comprise extended control signals to initiate operations on extension registers 210.

[0074] It will be appreciated that extension register file 214 may further include registers of two hundred and fifty-six bits or of five hundred and twelve bits, or that extension registers 210 may be combined with registers of two hundred and fifty-six bits or of five hundred and twelve bits or of any other convenient size to be addressed as part of or as a combination of the combined registers according to control signal 207.

[0075]FIG. 3a illustrates a general operation for one embodiment of processor 109. That is, FIG. 3 illustrates the process followed by processor 109 while performing an operation on packed data, performing an operation on unpacked data, or performing some other operation. For example, such operations include a load operation to load a register in register file 204 with data from cache 206, main memory 104, read only memory (ROM) 106, or data storage device 107. In one embodiment of the present invention, processor 109 supports most of the instructions supported by the Intel 80486™, available from Intel Corporation of Santa Clara, Calif. In another embodiment of the present invention, processor 109 supports all the operations supported by the Intel 80486™, available from Intel Corporation of Santa Clara, Calif. In another embodiment of the present invention, processor 109 supports all the operations supported by the Pentium™ processor, the Intel 80486™ processor, the 80386™ processor, the Intel 80286™ processor, and the Intel 8086™ processor, all available from Intel Corporation of Santa Clara, Calif. In another embodiment of the present invention, processor 109 supports all the operations supported in the IA™-Intel® Architecture, as defined by Intel Corporation of Santa Clara, Calif. (see Microprocessors, Intel Data Books volume 1 and volume 2, 1992 and 1993, available from Intel of Santa Clara, Calif.). Generally, processor 109 can support the present instruction set for the Pentium™ processor, but can also be modified to incorporate future instructions, as well as those described herein. What is important is that processor 109 can support previously used operations in addition to the operations described herein.

[0076] In processing block 301, the decoder 202 receives a control signal 207 from either the cache 206 or bus 101. Decoder 202 decodes the control signal to determine the operations to be performed.

[0077] Decoder 202 accesses the register file 204, or a location in another memory, in processing block 302. Registers in the register file 204, or memory locations in another memory, are accessed depending on the register address specified in the control signal 207. For example, for an operation on packed data, control signal 207 can include SRC1, SRC2 and DEST register addresses. SRC1 is the address of the first source register. SRC2 is the address of the second source register. In some cases, the SRC2 address is optional as not all operations require two source addresses. If the SRC2 address is not required for an operation, then only the SRC1 address is used. DEST is the address of the destination register where the result data is stored. In one embodiment, SRC1 or SRC2 is also used as DEST. SRC1, SRC2 and DEST are described more fully in relation to FIG. 6a through FIG. 6e. The data stored in the corresponding registers is referred to as Source1, Source2, and Result respectively.

[0078] In another embodiment of the present invention, any one, or all, of SRC1, SRC2 and DEST, can define a memory location in the addressable memory space of processor 109. For example, SRC1 may identify a memory location in main memory 104 while SRC2 identifies a first register in integer registers 201, and DEST identifies a second register in registers 209. For simplicity of the description herein, references are made to the accesses to the register file 204, however, these accesses could be made to another memory instead.

[0079] In another embodiment of the present invention, the operation code only includes two addresses, SRC1 and SRC2. In this embodiment, the result of the operation is stored in the SRC1 or SRC2 register. That is SRC1 (or SRC2) is used as the DEST. This type of addressing is compatible with previous CISC instructions having only two addresses. This reduces the complexity in the decoder 202. Note, in this embodiment, if the data contained in the SRC1 register is not to be destroyed, then that data is copied into another register before the execution of the operation. The copying would require an additional instruction. To simplify the description herein, the three address addressing scheme will be described (i.e. SRC1, SRC2, and DEST). However, it should be remembered that the control signal, in one embodiment, may only include SRC1 and SRC2, and that SRC1 (or SRC2) identifies the destination register.

[0080] Where the control signal requires an operation, in processing block 303, functional unit 203 will be enabled to perform this operation on accessed data from register file 204. Once the operation has been performed in functional unit 203, in processing block 304, the result is stored back into register file 204 or another memory according to requirements of control signal 207.

[0081] In one embodiment of processor 109, control signal 207 may comprise extended control signals for manipulating data in extension registers 210. FIG. 3b illustrates an alternative embodiment of a process to manipulate data in extension registers 210 of an extended register file 214. In processing block 311, the decoder 202 receives an extended control signal 207 from either the cache 206 or bus 101. Decoder 202 decodes the extended control signal to determine the operations to be performed and registers to be addressed. Decoder 202 accesses the extension registers 210, or a location in another memory, at processing block 312. Registers in the extension registers 210, or memory locations in another memory, are accessed depending on the extension register address specified in the extended control signal 207. For example, for an operation on one hundred and twenty-eight bit packed data, extended control signal 207 can include SRC1, SRC2 and DEST extension register addresses. In one embodiment of processor 109, the operation code only includes two addresses, SRC1 and SRC2. In this embodiment, the result of the operation is stored in the SRC1 (or SRC2) register, which is used as the DEST register.

[0082] Where the extended control signal requires an operation, in processing block 313, functional unit 203 will be enabled to perform this operation on accessed data from extension registers 210. Once the operation has been performed in functional unit 203, in processing block 314, the result is stored back into extension registers 210 or another memory according to requirements of extended control signal 207.

[0083] It will be appreciated that one embodiment of processor 109 may accept a control signal 207 that comprises control signals to initiate the execution of operations on packed data stored in registers 209 but may not need to accept a control signal 207 that also comprises extended control signals to initiate the execution of operations on packed data stored in extension registers 210. For this embodiment of processor 109, an application may need to request, for example, whether processor 109 will accept extended control signals and to install the appropriate control signals in accordance with which type of control signal 207 processor 109 will accept.

[0084] Software Enablement in a System

[0085] In order for an application to more fully utilize the extended register file 214 and to initiate the execution of operations on packed data stored in extension registers XR₀ 213 a through XR₇ 213 h, it may be necessary for the processor 109 to coordinate with the application or with the operating system of computer system 100 to provide a permission signal to the application or to the operating system enabling the application or operating system to submit extended control signals, the extended control signals initiating operations on packed data stored in extension registers XR₀ 213 a through XR₇ 213 h. The application or operating system, having received the permission signal from processor 109, may manipulate data in a register file in accordance with the process of FIG. 3b. Alternatively, the application or operating system may manipulate data in a register file in accordance with FIG. 3 a.

[0086]FIG. 3c illustrates one embodiment of a process for a processor to enable application software or operating system software to manipulate data in extended register file 214. In processing block 321 a request to submit extended control signals is received by processor 109 from an application or an operating system of computer system 100. In processing block 322, processor 109 provides a permission signal to the application or an operating system of computer system 100 indicating that the application or operating system may manipulate data in a register file in accordance with the process of FIG. 3b.

[0087] It will be appreciated that the permission signal may be provided through any one of a number of methods. For example, in one embodiment of processor 109 that supports a set of operations supported by the Pentium™ processor, bit twenty-six in the EDX register of integer registers 201 is set to a value of 1 in response to a CPUID request from the application or from the operating system. The setting of this particular bit may be understood as providing the requested permission signal in accordance with procedures defined by Intel Corporation of Santa Clara, Calif. (see Chapter 3 of the IA-32 Intel® Architecture Software Developer's Manual, Volume 2, Order Number 245471; and AP-485, Intel Processor Identification and the CPUID Instruction, Order Number 241618; both available from Intel of Santa Clara, Calif. or online at http://developer.intel.com).

[0088] Having received the permission signal from processor 109, the application or operating system of computer system 100 may have further need of coordinating communication. For example, the operating system of computer system 100 may or may not be enabled to save and restore the state of extension registers 210 in the event of a context switch in a multitasking environment, or during calls and returns from interrupt or exception handlers. The desired communication may be facilitated by processor 109 to enable an operating system of computer system 100 to communicate, to the application software, a state of readiness or non-readiness for supporting manipulation of data in accordance with the process of FIG. 3b.

[0089] In processing block 323, processor 109 receives a request to access a control register. For example, in one embodiment of processor 109 that supports a set of operations supported by the Pentium™ processor, access to CR4 of status registers 208 is requested. In processing block 324, processor 109 provides access the requested control register (see Chapter 11 of the IA-32 Intel® Architecture Software Developer's Manual, Volume 1, Order Number 245470; available from Intel of Santa Clara, Calif. or online at http://developer.intel.com).

[0090] It will be appreciated that communication between the operating system and the application may be facilitated by processor 109 providing read or write access to a control register through any one of a number of methods. For example, in one embodiment of processor 109 that supports a set of operations supported by the Pentium™ processor, bit nine in the CR4 register of status registers 208 is set to a value of 1 in response to a request from the operating system of computer system 100 to indicate that the operating system supports an FXSAVE and an FXRSTOR instruction to save and to restore, respectively, the state of extension registers 210 in the event of a context switch. Alternatively, processor 109 may provide access to the CR4 register of status registers 208 responsive to a MOV instruction request by the application software to read the contents of CR4. Upon checking the contents of control register CR4 and finding bit nine set to a value of 1, the application may manipulate data in a register file in accordance with the process of FIG. 3b. Alternatively, upon finding bit nine of CR4 set to zero, the application may manipulate data in a register file in accordance with FIG. 3a.

[0091] Data Storage and Formats

[0092]FIG. 4a illustrates some of the data formats as may be used in the computer system of FIG. 1. These data formats are fixed point. Processor 109 can manipulate these data formats. Multimedia algorithms often use these data formats. A byte 401 contains eight bits of information. A word 402 contains sixteen bits of information, or two bytes. A doubleword 403 contains thirty-two bits of information, or four bytes. A quadword 404 contains sixty-four bits of information, or eight bytes. A double quadword 405 contains one hundred and twenty-eight bits of information, or sixteen bytes. Thus, processor 109 executes control signals that may operate on any one of these memory data formats.

[0093] In the following description, references to bit, byte, word, doubleword, and quadword subfields are made. For example, bit six through bit zero of the byte 00111010₂ (shown in base 2) represent the subfield 111010 ₂. For the simplicity of the description, FIG. 4b through FIG. 4d describe the representations of some frequently used data formats in sixty-four bit registers, however, thirty-two bit registers, one hundred and twenty-eight bit registers, or registers of any other convenient size may also be used.

[0094]FIG. 4b through FIG. 4d illustrate in-register representations used in one embodiment of the present invention. For example, unsigned byte in-register representation 410 can represent data stored in a register in integer registers 201. In one embodiment, a register in integer registers 201 is sixty-four bits in length. In another embodiment, a register in integer registers 201 is thirty-two bits in length. In other embodiments, other sizes of registers may be used.

[0095] Unsigned byte in-register representation 410 illustrates processor 109 storing an unsigned byte in integer registers 201. The first eight bits, bit seven through bit zero, in that register are dedicated to the data byte 401. These bits are shown as {b}. To properly represent this byte, the remaining 56 bits must be zero. For a signed byte in-register representation 411, integer registers 201 store the magnitude of a signed byte in the first seven bits, bit six through bit zero. The seventh bit represents the sign bit, shown as an {s}. Each of the remaining bits, bit sixty-three through bit eight, contain the sign bit.

[0096] Unsigned word in-register representation 412 is stored in one register of integer registers 201. Bit fifteen through bit zero contain an unsigned word. These bits are shown as {w}. To properly represent this word, the remaining bit sixty-three through bit sixteen must be zero. The magnitude of a signed word is stored in bit fourteen through bit zero as shown in the signed word in-register representation 413. Each of the remaining bits, bit sixty-three through bit fifteen, contain the sign bit.

[0097] A doubleword can be stored as an unsigned doubleword in-register representation 414 or a signed doubleword in-register representation 415. Bit thirty-one through bit zero of an unsigned doubleword in-register representation 414 contain an unsigned doubleword. These bits are shown as {d}. To properly represent this unsigned doubleword, the remaining bit sixty-three through bit thirty-two must be zero. Integer registers 201 stores the magnitude of a signed doubleword in bit thirty through bit zero as shown in signed doubleword in-register representation 415. Each of the remaining bits, bit sixty-three through bit thirty-one, contain the sign bit.

[0098] As indicated by the above FIG. 4b through FIG. 4d, storage of some data types in a sixty-four bit wide register is an inefficient method of storage. For example, for storage of an unsigned byte in-register representation 410 bit sixty-three through bit eight must be zero, while only bit seven through bit zero may contain non-zero bits. Thus, a processor storing a byte in a sixty-four bit register uses only 12.5% of the register's capacity. Similarly, only the first few bits of operations performed by functional unit 203 will be important.

[0099]FIG. 5a illustrates the data formats for one embodiment of packed data types. Three packed data formats are illustrated; packed byte 501, packed word 502, and packed doubleword 503. Packed byte, in this embodiment, is sixty-four bits long containing eight data elements. Each data element is one byte long. Generally, a data element is an individual piece of data that is stored in a single register (or memory location) with other data elements of the same length. In this embodiment, the number of data elements stored in a register is sixty-four bits divided by the length in bits of a data element. It will be appreciated that alternative embodiments may include registers having a capacity for storing more bits or for storing less bits, and that these registers may store data in more packed data formats or in less packed data formats than those illustrated in FIG. 5a.

[0100] Packed word 502 is sixty-four bits long and contains four word 402 data elements. Each word 402 data element contains sixteen bits of information.

[0101] Packed doubleword 503 is sixty-four bits long and contains two doubleword 403 data elements. Each doubleword 403 data element contains thirty-two bits of information.

[0102]FIG. 5b illustrates one alternative embodiment of packed data-types. In this embodiment, Four packed data formats are illustrated; packed byte 504, packed word 505, packed doubleword 506, and packed quadword 507. Packed byte 504, in this embodiment, is one hundred and twenty-eight bits long containing sixteen byte 401 data elements. Each data element is one byte long. In this embodiment, the number of data elements stored in a register is one hundred and twenty-eight bits divided by the length in bits of a data element. It will be appreciated that alternative embodiments including registers with a capacity for storing more bits may or may not include additional packed data formats—for example packed double quadwords, or packed 2-dimensional pixels (or 3-dimensional voxels) of various sizes.

[0103] Packed word 505 is one hundred and twenty-eight bits long and contains eight word 402 data elements. Each word 402 data element contains sixteen bits of information.

[0104] Packed doubleword 506 is one hundred and twenty-eight bits long and contains four doubleword 403 data elements. Each doubleword 403 data element contains thirty-two bits of information.

[0105] Packed quadword 507 is one hundred and twenty-eight bits long and contains two quadword 404 data elements. Each quadword 404 data element contains sixty-four bits of information.

[0106]FIG. 5c through FIG. 5e illustrate one embodiment of in-register packed data storage representations. For simplicity, sixty-four bit in-register packed data storage representations are illustrated, however, one hundred and twenty-eight bit in-register packed data storage representations or in-register packed data storage representations of other convenient sizes may also be used.

[0107] Unsigned packed byte in-register representation 510 illustrates the storage of packed byte 501 data, for example, in one of the registers R₀ 212 a through R₇ 212 h. Information for each byte data element is stored in bit seven through bit zero for byte zero, bit fifteen through bit eight for byte one, bit twenty-three through bit sixteen for byte two, bit thirty-one through bit twenty-four for byte three, bit thirty-nine through bit thirty-two for byte four, bit forty-seven through bit forty for byte five, bit fifty-five through bit forty-eight for byte six and bit sixty-three through bit fifty-six for byte seven. Thus, all available bits are used in the register. This storage arrangement increases the storage efficiency of the processor. As well, with eight data elements accessed, one operation can now be performed on eight data elements simultaneously. Signed packed byte in-register representation 511 is similarly stored in a register in registers 209. Note that only the eighth bit of every byte data element is the necessary sign bit; other bits may or may not be used to indicate the sign as dictated by the magnitude of the number being represented.

[0108] In an alternative embodiment, a one hundred and twenty-eight bit packed byte in-register representation for storage of packed byte 504 data, for example, in one of the registers XR₀ 213 a through XR₇ 213 h, would additionally allocate bit seventy-one through bit sixty-four for byte eight, bit seventy-nine through bit seventy-two for byte nine, bit eighty-seven through bit eighty for byte ten, bit ninety-five through bit eighty-eight for byte eleven, bit one hundred and three through bit ninety-six for byte twelve, bit one hundred and eleven through bit one hundred and four for byte thirteen, bit one hundred and nineteen through bit one hundred and twelve for byte fourteen and bit one hundred and twenty-seven through bit one hundred and twenty for byte fifteen.

[0109] Unsigned packed word in-register representation 512 illustrates how word three through word zero are stored in one register of registers 209. Bit fifteen through bit zero contain the data element information for word zero, bit thirty-one through bit sixteen contain the information for data element word one, bit forty-seven through bit thirty-two contain the information for data element word two and bit sixty-three through bit forty-eight contain the information for data element word three. Signed packed word in-register representation 513 is similar to the unsigned packed word in-register representation 512. Note that only the sixteenth bit of each word data element needs to contain the sign indicator. Use of any of the other fifteen bits is dictated by the magnitude of the number being represented.

[0110] In an alternative embodiment, a one hundred and twenty-eight bit packed word in-register representation for storage of packed word 505 data, for example, in one of the extension registers 210, would additionally allocate bit seventy-nine through bit sixty-four for word four, bit ninety-five through bit eighty for word five, bit one hundred and eleven through bit ninety-six for word six, and bit one hundred and twenty-seven through bit one hundred and twelve for word seven.

[0111] Unsigned packed doubleword in-register representation 514 shows how registers 209 store two doubleword data elements. Doubleword zero is stored in bit thirty-one through bit zero of the register. Doubleword one is stored in bit sixty-three through bit thirty-two of the register. Signed packed doubleword in-register representation 515 is similar to unsigned packed doubleword in-register representation 514. Note that the necessary sign bit is the thirty-second bit of the doubleword data element.

[0112] In an alternative embodiment, a one hundred and twenty-eight bit packed doubleword in-register representation for storage of packed doubleword 506 data in one of the extension registers 210, would additionally allocate bit ninety-five through bit sixty-four for doubleword two, and bit one hundred and twenty-seven through bit ninety-six for doubleword three.

[0113]FIG. 5f illustrates one embodiment of a packed quadword in-register representation. Unsigned packed quadword in-register representation 516 shows how extension registers 210 store two quadword data elements. Quadword zero is stored in bit sixty-three through bit zero of the register. Quadword one is stored in bit one hundred and twenty-seven through bit sixty-four of the register. Signed packed quadword in-register representation 517 is similar to unsigned packed quadword in-register representation 516. Note that the necessary sign bit is the sixty-fourth bit of the quadword data element.

[0114] As mentioned previously, registers may be used for both packed data and integer data. In one embodiment of processor 109, the individual programming processor 109 may be required to track whether an addressed register, R₀ 212 a for example, is storing packed data or simple integer/fixed point data. In an alternative embodiment, processor 109 could track the type of data stored in individual registers of registers 209. This alternative embodiment could then generate errors if, for example, a packed addition operation were attempted on simple/fixed point integer data.

[0115] Control Signal Formats

[0116] The following describes one embodiment of control signal formats used by processor 109 to manipulate packed data. In this embodiment, control signals are represented as thirty-two bits. Decoder 202 may receive control signal 207 from bus 101. In another embodiment, decoder 202 can also receive such control signals from cache 206.

[0117]FIG. 6a illustrates a general format for a control signal operating on packed data. Operation field OP 601, bit thirty-one through bit twenty-six, provides information about the operation to be performed by processor 109; for example, packed addition, packed subtraction, etc. SRC1 602, bit twenty-five through twenty, provides the source register address of a register in registers 209. This source register contains the first packed data, Source1, to be used in the execution of the control signal. Similarly, SRC2 603, bit nineteen through bit fourteen, contains the address of a register in registers 209. This second source register contains the packed data, Source2, to be used during execution of the operation. DEST 605, bit five through bit zero, contains the address of a register in registers 209. This destination register will store the result packed data, Result, of the packed data operation.

[0118] Control bits SZ 610, bit twelve and bit thirteen, indicates the length of the data elements in the first and second packed data source registers. If SZ 610 equals 01₂, then the packed data is formatted as packed byte 501. If SZ 610 equals 10₂, then the packed data is formatted as packed word 502. SZ 610 equaling 00₂ or 11₂ is reserved, however, in another embodiment, one of these values could be used to indicate that the packed data is to be formatted as a packed doubleword 503.

[0119] Control bit T 611, bit eleven, indicates whether the operation is to be carried out with saturate mode. If T 611 equals one, then a saturating operation is performed. If T 611 equals zero, then a nonsaturating operation is performed. Saturating operations will be described later.

[0120] Control bit S 612, bit ten, indicates the use of a signed operation. If S 612 equals one, then a signed operation is performed. If S 612 equals zero, then an unsigned operation is performed.

[0121] In one alternative embodiment, control signals may have any one of a plurality of lengths. Decoder 202 may receive one or more format type of control signal 207 from bus 101. In another embodiment, decoder 202 can also receive format types of control signal 207 from cache 206 that are similar to or different from the format types of control signal 207 received from bus 101. In another embodiment, receipt of a first format type of controls signal 207 from bus 101, may cause processor 109 to execute one or more of a second set of format types of control signal 207 to perform the operation of the control signal 207 received from bus 101.

[0122]FIG. 6b, FIG. 6c, FIG. 6d and FIG. 6e illustrate alternative embodiments of a control signal format that may be used, for example, in computer system 100 to initiate an operation on packed data.

[0123]FIG. 6b illustrates one embodiment of a control signal format that corresponds with the general integer instruction format described in the Pentium™ Processor Family User's Manual, available from Intel Corporation, Literature Sales, P.O. Box 7641, Mt. prospect, Ill., 60056-7641. Note that OP 601, SZ 610, T 611, and S 612 are all combined into one large field. For some control signals, bits three through five are SRC1 602. In one embodiment, where there is a SRC1 602 address, then bits three through five also correspond to DEST 605. In an alternate embodiment, where there is a SRC2 603 address, then bits zero through two also correspond to DEST 605. For other control signals, like a packed shift immediate operation, bits three through five represent an extension to the opcode field. In one embodiment, this extension allows a programmer to include an immediate value with the control signal, such as a shift count value. In one embodiment, the immediate value follows the control signal. This is described in more detail in the Pentium™ Processor Family User's Manual, in appendix F, pages F-1 through F-3. Bits zero through two represent SRC2 603. This general format allows register to register, memory to register, register by memory, register by register, register by immediate, and register to memory addressing. Also, in one embodiment, this general format can support integer register to register, and register to integer register addressing.

[0124]FIG. 6c illustrates an alternative embodiment of a control signal format that corresponds with the general integer instruction format described in the IA-32 Intel® Architecture Software Developer's Manual, Volume 2, Order Number 245471; available from Intel Corporation or online at http://developer.intel.com. This embodiment comprises four or more bytes. In addition to the control signal format of FIG. 6b, the control signal format of FIG. 6c includes a prefix 613. For some control signals, prefix 613 may be used by decoder 202 to identify a SRC1 602 address or a SRC2 603 address in integer registers 201 or in registers 209. For some control signals, prefix 613 may be used by decoder 202 to identify a SRC2 603 address in extension registers 210. For some control signals, prefix 613 may be used by decoder 202 to identify a SRC1 602 address in extension registers 210. In one embodiment, where there is a SRC1 602 address, then bits three through five also correspond to DEST 605. In another embodiment, where there is a SRC2 603 address, then bits zero through two also correspond to DEST 605. In one embodiment, decoder 202 may enable functional unit 203 to perform a one hundred and twenty-eight bit packed data operation in response to decoding prefix 613. In another embodiment, decoder 202 may enable functional unit 203 to perform an operation on less than all of the elements of a one hundred and twenty-eight bit packed data in response to decoding prefix 613.

[0125]FIG. 6d illustrates another alternative embodiment of a control signal format that corresponds with the general integer instruction format described in the IA-32 Intel® Architecture Software Developer's Manual, Volume 2, from Intel Corporation. This embodiment comprises four or more bytes. For some control signals, bits eight through ten are SRC1 602. In one embodiment, where there is a SRC1 602 address, then bits eight through ten also correspond to DEST 605. In addition to the control signal format of FIG. 6b, the control signal format of FIG. 6d includes an extension EXT 614. In one embodiment, bits eight through fifteen are referred to as a ModR/M byte, bits zero through two of the ModR/M byte corresponding to SRC1 602, and bits three through five of the ModR/M byte (bits eleven through thirteen of FIG. 6d) corresponding to EXT 614. For some control signals, EXT 614 may be used by decoder 202 to identify an immediate Source2 604. In one embodiment, the immediate Source2 604 is identified with bits zero through seven.

[0126]FIG. 6e illustrates another alternative embodiment of a control signal format that corresponds with the general integer instruction format described in the IA-32 Intel® Architecture Software Developer's Manual, Volume 2, from Intel Corporation. This embodiment comprises five or more bytes. For some control signals, bits eight through ten are SRC1 602. In one embodiment, where there is a SRC1 602 address, then bits eight through ten also correspond to DEST 605. Like the control signal format of FIG. 6d, the control signal format of FIG. 6e includes an extension EXT 614, and bits eight through fifteen may be referred to as a ModR/M byte, with bits zero through two of the ModR/M byte corresponding to SRC1 602, and bits three through five of the ModR/M byte corresponding to EXT 614.

[0127] In addition to the control signal format of FIG. 6d, the control signal format of FIG. 6e includes a prefix 613. For some control signals, prefix 613 may be used by decoder 202 to identify a SRC1 602 address in extension registers 210. In one embodiment, where there is a SRC1 602 address, then bits three through five (or bits zero through two of the ModR/M byte) also correspond to DEST 605. In one embodiment, decoder 202 may enable functional unit 203 to perform a one hundred and twenty-eight bit packed data operation at least partially in response to decoding prefix 613. For some control signals, EXT 614 may be used by decoder 202 to identify an immediate Source2 604. In one embodiment, the immediate Source2 604 is identified with bits zero through seven. In an alternative embodiment, decoder 202 may enable functional unit 203 to perform a one hundred and twenty-eight bit packed data operation or a one hundred and twenty-eight bit scalar operation at least partially in response to decoding EXT 614. In another alternative embodiment, decoder 202 may enable functional unit 203 to scale or translate the value of immediate Source2 604 at least partially in response to decoding EXT 614.

[0128] For example, a list of possible control signal encodings for shift operations using one embodiment of the control signals formats of FIG. 6b, FIG. 6c, FIG. 6d and FIG. 6e is shown in Table 1. TABLE 1 Instruction Prefix 613 OPCODE - Format[bits] EXT 614 SRC1 SRC2 1 PSLLW N/A 0F F1 - FIG. 6b[23:8] N/A 209 209/M 2 PSLLW 66 0F F1 - FIG. 6c[23:8] N/A 210 210/M 3 PSLLW N/A 0F 71 - FIG. 6d[31:16] 6 209 I-bits 4 PSRLW N/A 0F 71 - FIG. 6d[31:16] 2 209 I-bits 5 PSLLD N/A 0F F2 - FIG. 6b[23:8] N/A 209 209/M 6 PSLLD 66 0F F2 - FIG. 6c[23:8] N/A 210 210/M 7 PSLLD 66 0F 72 - FIG. 6e[31:16] 6 210 I-bits 8 PSRLD 66 0F 72 - FIG. 6e[31:16] 2 210 I-bits 9 PSLLQ N/A 0F F3 - FIG. 6b[23:8] N/A 209 209/M 10 PSLLQ 66 0F F3 - FIG. 6c[23:8] N/A 210 210/M 11 PSLLQ N/A 0F 73 - FIG. 6d[31:16] 6 209 I-bits 12 PSLLQ 66 0F 73 - FIG. 6e[31:16] 6 210 I-bits 13 PSLLDQ 66 0F 73 - FIG. 6e[31:16] 7 210 I-bytes 14 PSRLQ N/A 0F F3 - FIG. 6b[23:8] N/A 209 209/M 15 PSRLQ 66 0F F3 - FIG. 6c[23:8] N/A 210 210/M 16 PSRLQ N/A 0F 73 - FIG. 6d[31:16] 2 209 I-bits 17 PSRLQ 66 0F 73 - FIG. 6e[31:16] 2 210 I-bits 18 PSRLDQ 66 0F 73 - FIG. 6e[31:16] 3 210 I-bytes

[0129] The entry on line 1 of Table 1 indicates that the Packed Shift Left Logical Words (PSLLW) instruction, with no prefix 613 and an operation code (OPCODE) having the hexadecimal value of 0F F1 (0000 1111 1111 0001₂) in bits twenty-three through eight of the format shown in FIG. 6b will identify a SRC1 address in registers 209 and a SRC2 address in registers 209 or in Memory. Referring to the entry on line 2 of Table 1, by using the format shown in FIG. 6c and employing a prefix 613 having a hexadecimal value of 66 (0110 0110₂), decoder 202 will identify a SRC1 address in registers 201 and a SRC2 address in extension registers 210 or in Memory. Referring to the entry on line 3 of Table 1, by using the format shown in FIG. 6d and employing an extension EXT 614 having a decimal value of 6 (1102), decoder 202 will identify a SRC1 address in registers 209 and an immediate Source2 value in bits seven through zero of control signal 207, and will enable functional unit 203 to perform a bitwise left logical shift of the packed words stored at SRC1 by the immediate Source2 value. Referring to the entry on line 4 of Table 1, by using the format shown in FIG. 6d and employing an extension EXT 614 having a decimal value of 2 (010₂), decoder 202 will enable functional unit 203 to perform a bitwise right logical shift (PSRLW) of the packed words stored at SRC1 in registers 209 by the immediate Source2 value.

[0130] Referring now to the entry on line 12 of Table 1, by using the format shown in FIG. 6e and employing a prefix 613 having a hexadecimal value of 66 (0110 0110₂), and an extension EXT 614 having a decimal value of 6 (1102) along with an OPCODE having the hexadecimal value of 0F 73 (0000 1111 0111 0011₂), decoder 202 will identify a SRC1 address in extension registers 210 and an immediate Source2 value in bits seven through zero of control signal 207, and will enable functional unit 203 to perform a bitwise left logical shift of the packed quadwords stored at SRC1 by the immediate Source2 value. On the other hand, referring to the entry on line 13 of Table 1, by using the same format of FIG. 6e and employing the same prefix 613 of 66 (0110 0110₂), but with an extension EXT 614 having a decimal value of 7 (111₂) and the same OPCODE of 0F 73 (0000 1111 0111 0011₂), decoder 202 will again identify a SRC1 address in extension registers 210 and an immediate Source2 value in bits seven through zero of control signal 207, but will enable functional unit 203 to perform a bytewise left logical shift of the packed double quadwords stored at SRC1 by the immediate Source2 value.

[0131] One embodiment of the control signal formats herein disclosed provide for a decoder 202 having reduced additional circuitry, area and cost. One embodiment of the control signal formats herein disclosed further provides for a decoder 202 for efficient decoding of control signals for previously used operations and extended control signals.

[0132] The foregoing disclosures are illustrated by way of example and not limitation with unnecessary detail omitted so as not to obscure the invention. It will be appreciated that the apparatuses and methods described above can be modified in arrangement and detail by those skilled in the art.

[0133] Description of Saturate/Unsaturate

[0134] As mentioned previously, T 611 indicates whether operations optionally saturate. Where the result of an operation, with saturate enabled, overflows or underflows the range of the data, the result is clamped. Clamping means setting the result to a maximum or minimum value should a result exceed the range's maximum or minimum value. In the case of underflow, saturation clamps the result to the lowest value in the range and in the case of overflow, to the highest value. The allowable range for each data format is shown in Table 2. TABLE 2 Data Format Minimum Value Maximum Value Unsigned Byte 0  255 Signed Byte −128  127 Unsigned Word 0 65535 Signed Word −32768 32767 Unsigned Doubleword 0 2⁶⁴−1 Signed Doubleword −2⁶³ 2⁶³−1

[0135] As mentioned above, T 611 indicates whether saturating operations are being performed. Therefore, using the unsigned byte data format, if an operation's result=258 and saturation was enabled, then the result would be clamped to 255 before being stored into the operation's destination register. Similarly, if an operation's result=−32999 and processor 109 used signed word data format with saturation enabled, then the result would be clamped to −32768 before being stored into the operation's destination register.

[0136] Shift Operation

[0137] In one embodiment of processor 109, the performance of CSC applications is improved by not only supporting a standard CISC instruction set (unpacked data operations), but by supporting a shift operation on packed data. The packed shift can be used to increase the speed of fixed-point implements of Fast Fourier Transforms, Cosine Transforms, and other digital image and audio signal processing algorithms.

[0138] In one embodiment of the shift operation, the SRC1 register contains the data (Source1) to be shifted, the SRC2 register contains the data (Source2) representing the shift count, and DEST register will contain the result of the shift (Result). That is, Source1 will have each data element independently shifted by the shift count. In one embodiment, Source2 is interpreted as an unsigned sixty-four bit scalar. In an alternative embodiment, Source2 is packed data and contains shift counts for each corresponding data element in Source1. In another alternative embodiment, Source2 is interpreted as being scaled or translated by some mapping or arithmetic formula or constant. For example, Source1 may be shifted by an number of byte positions, the number of positions indicated directly of indirectly by Source2.

[0139] In one embodiment of the present invention, both arithmetic shifts and logical shifts are supported. An arithmetic shift, shifts the bits of each data element down by a specified number, and fills the high order bit of each data element with the initial value of the sign bit. A shift count greater than seven for packed byte data, greater than fifteen for packed word data, greater than thirty-one for packed doubleword, greater than sixty-three for packed quadword, or greater than one hundred and twenty-seven for packed double quadword causes each Result data element to be filled with the initial value of the sign bit. A logical shift can operate by shifting bits up or down. In a shift right logical, the high order positions of each data element are filled with zeroes. A shift left logical causes the least significant positions of each data element to be filled with zeroes.

[0140] In one embodiment, a shift right arithmetic, a shift right logical, and a shift left logical operation are supported for packed bytes and packed words. In an alternative embodiment, these operations are supported for packed doublewords also. In another alternative embodiment, some shift operations are also supported for packed quadwords and double quadwords.

[0141]FIG. 7a illustrates one embodiment of a process for performing shift operations on packed data stored in registers 209. This embodiment can be implemented in the processor 109 of FIG. 2a or FIG. 2b.

[0142] In processing block 701, decoder 202 decodes control signal 207 received by processor 109. Thus, decoder 202 decodes: the operation code for the appropriate shift operation; SRC1 602, SRC2 603 and DEST 605 addresses in registers 209; saturate/unsaturate (not necessarily needed for shift operations), signed/unsigned (again not necessarily needed), and length of the data elements in the packed data.

[0143] In processing block 702, via internal bus 205, decoder 202 accesses registers 209 in register file 204 or extended register file 214 given the SRC1 602 and SRC2 603 addresses. Registers 209 provide functional unit 203 with the packed data stored in the SRC1 602 register (Source1), and the scalar shift count (Source2) stored in SRC2 603 register or control signal 207. That is, integer registers 209 communicate the packed data to functional unit 203 via internal bus 205.

[0144] In processing block 703, decoder 202 enables functional unit 203 to perform the appropriate packed shift operation. Decoder 202 further communicates, via internal bus 205, the size of data elements, the type of shift operation, and the direction of the shift (for logical shifts).

[0145] For this embodiment in processing block 710, the size of the data element determines which processing block is to be executed next. If the size of the data elements is eight bits (byte data), then functional unit 203 performs the operation of processing block 712. However, if the size of the data elements in the packed data is sixteen bits (word data), then functional unit 203 performs the operation of processing block 714. In one embodiment, only eight bit and sixteen bit data element size packed shifts are supported. However, in another embodiment, a thirty-two bit data element size packed shift is also supported. In other embodiments, other size data elements may be supported.

[0146] Assuming the size of the data elements is eight bits, then processing block 712 is executed. In processing block 712, the following is performed. Source1 bits seven through zero are shifted by the shift count (Source2 bits sixty-three through zero) generating Result bits seven through zero. Source1 bits fifteen through eight are shifted by the shift count generating Result bits fifteen through eight. Source1 bits twenty-three through sixteen are shifted by the shift count generating Result bits twenty-three through sixteen. Source1 bits thirty-one through twenty-four are shifted by the shift count generating Result bits thirty-one through twenty-four. Source1 bits thirty-nine through thirty-two are shifted by the shift count generating Result bits thirty-nine through thirty-two. Source1 bits forty-seven through forty are shifted by the shift count generating Result forty-seven through forty. Source1 bits fifty-five through forty-eight are shifted by the shift count generating Result bits fifty-five through forty-eight. Source1 bits sixty-three through fifty-six are shifted by the shift count generating Result bits sixty-three through fifty-six.

[0147] Assuming the size of the data elements is sixteen bits, then processing block 714 is executed. In processing block 714, the following is performed. Source1 bits fifteen through zero are shifted by the shift count generating Result bits fifteen through zero. Source1 bits thirty-one through sixteen are shifted by the shift count generating Result bits thirty-one through sixteen. Source1 bits forty-seven through thirty-two are shifted by the shift count generating Result bits forty-seven through thirty-two. Source1 bits sixty-three through forty-eight are shifted by the shift count generating Result bits sixty-three through forty-eight.

[0148] In one embodiment, the shifts of processing block 712 are performed simultaneously. However, in another embodiment, these shifts are performed serially. In another embodiment, some of these shifts are performed simultaneously and some are performed serially. This discussion applies to the shifts of processing block 714 as well.

[0149] At processing block 720, the Result is stored in the DEST register.

[0150]FIG. 7b illustrates an alternative embodiment of a process for performing shift operations on packed data stored in extension registers 210. This embodiment can be implemented in the processor 109 of FIG. 2b.

[0151] In processing block 721, decoder 202 decodes control signal 207 received by processor 109, control signal 207 having an extended control signal format for performing shift operations on extension registers 210. Thus, decoder 202 decodes: the operation code for the appropriate shift operation; the location of Sourc2 and SRC1 602 and DEST 605 addresses in registers 210; saturate/unsaturate (not necessarily needed for shift operations), signed/unsigned (again not necessarily needed), length of the data elements, and type of shift positions.

[0152] In processing block 722, via internal bus 205, decoder 202 accesses extension registers 210 in register file 214 given the SRC1 602 and possible SRC2 603 addresses. Registers 210 provide functional unit 203 with the packed data stored in the SRC1 602 register (Source1), and the scalar shift count (Source2) stored in SRC2 603 register or in control signal 207. That is, extension registers 210 communicate the packed data to functional unit 203 via internal bus 205.

[0153] Decoder 202 proceeds to enable functional unit 203 to perform the appropriate shift operation communicating via internal bus 205, the size of data elements, the type of shift operation, the number and type of shift positions and the direction of the shift (for logical shifts).

[0154] If the control signal format of control signal 207 includes a SRC2 603 address in processing block 730, then the register in extension registers 210 at address SRC2 603 is accessed and the shift count data Source2 is communicated to functional unit 203 in accordance with processing block 724 and processing continues in processing block 732. Otherwise, if an immediate Source2 shift count is provided in the control signal format of control signal 207, then the immediate Source2 data is communicated to functional unit 203 in accordance with processing block 723, and processing continues in processing block 731.

[0155] In processing block 731, the type of shift positions determines which processing block is to be executed next. If the set of data elements are to be shifted by byte positions, then functional unit 203 performs the operation of processing block 725. However, if the set of data elements are to be shifted by bit positions, then processing continues in processing block 732. In one embodiment, shifting by byte positions is only supported for one hundred and twenty-eight bit data elements (double quadword data). However, in another embodiment, shifting by byte positions for sixty-four bit data elements (quadword data) is also supported. In other embodiments, shifting by byte positions of other size data elements may be supported.

[0156] Assuming the size of the data elements is one hundred and twenty-eight bits, then processing block 725 is executed. In processing block 725, the Source1 bytes fifteen through zero are shifted by the number of byte positions in the shift count (Source2) generating Result bytes fifteen through zero.

[0157] In processing block 732, the size of the data elements determines which processing block is to be executed next. If the size of the data elements is sixty-four bits (quadword data), then functional unit 203 performs the operation of processing block 726. Alternatively, if the size of the data elements is thirty-two bits (doubleword data), then functional unit 203 performs the operation of processing block 727. In a third alternative, if the size of the data elements is sixteen bits (word data), then functional unit 203 performs the operation of processing block 728. Finally, if the size of the data elements is eight bits (byte data), then functional unit 203 performs the operation of processing block 729.

[0158] Assuming the size of the data elements is sixty-four bits, then processing block 726 is executed. In processing block 726, the following is performed. The Source1 bits sixty-three through zero are shifted by the number of bit positions in the shift count (Source2) generating Result bits sixty-three through zero. The Source1 bits one hundred and twenty-eight through sixty-four are shifted by the number of bit positions in the shift count (Source2) generating Result bits one hundred and twenty-eight through sixty-four.

[0159] Assuming the size of the data elements is thirty-two bits, then processing block 727 is executed. In processing block 727, the following is performed. The Source1 bits thirty-one through zero are shifted by the number of bit positions in the shift count (Source2) generating Result bits thirty-one through zero. The Source1 bits sixty-three through thirty-two are shifted by the number of bit positions in the shift count (Source2) generating Result bits sixty-three through thirty-two. The Source1 bits ninety-five through sixty-four are shifted by the number of bit positions in the shift count (Source2) generating Result bits ninety-five through sixty-four. The Source1 bits one hundred and twenty-eight through ninety-six are shifted by the number of bit positions in the shift count (Source2) generating Result bits one hundred and twenty-eight through ninety-six.

[0160] Assuming the size of the data elements is sixteen bits, then processing block 728 is executed. In processing block 728, the following is performed. The Source1 bits fifteen through zero are shifted by the number of bit positions in the shift count (Source2) generating Result bits fifteen through zero. The Source1 bits thirty-one through sixteen are shifted by the number of bit positions in the shift count (Source2) generating Result bits thirty-one through sixteen. The Source1 bits forty-seven through thirty-two are shifted by the number of bit positions in the shift count (Source2) generating Result bits forty-seven through thirty-two. The Source1 bits sixty-three through forty-eight are shifted by the number of bit positions in the shift count (Source2) generating Result bits sixty-three through forty-eight. The Source1 bits seventy-nine through sixty-four are shifted by the number of bit positions in the shift count (Source2) generating Result bits seventy-nine through sixty-four. The Source1 bits ninety-five through eighty are shifted by the number of bit positions in the shift count (Source2) generating Result bits ninety-five through eighty. The Source1 bits one hundred and eleven through ninety-six are shifted by the number of bit positions in the shift count (Source2) generating Result bits one hundred and eleven through ninety-six. The Source1 bits one hundred and twenty-eight through one hundred and eleven are shifted by the number of bit positions in the shift count (Source2) generating Result bits one hundred and twenty-eight through one hundred and eleven.

[0161] Assuming the size of the data elements is eight bits, then processing block 729 is executed. In processing block 729, the following is performed. Source1 bits seven through zero are shifted by the number of bit positions in the shift count (Source2) generating Result bits seven through zero. Source1 bits fifteen through eight are shifted by the number of bit positions in the shift count (Source2) generating Result bits fifteen through eight. Source1 bits twenty-three through sixteen are shifted by the number of bit positions in the shift count (Source2) generating Result bits twenty-three through sixteen. Source1 bits thirty-one through twenty-four are shifted by the number of bit positions in the shift count (Source2) generating Result bits thirty-one through twenty-four. Source1 bits thirty-nine through thirty-two are shifted by the number of bit positions in the shift count (Source2) generating Result bits thirty-nine through thirty-two. Source1 bits forty-seven through forty are shifted by the number of bit positions in the shift count (Source2) generating Result forty-seven through forty. Source1 bits fifty-five through forty-eight are shifted by the number of bit positions in the shift count (Source2) generating Result bits fifty-five through forty-eight. Source1 bits sixty-three through fifty-six are shifted by the number of bit positions in the shift count (Source2) generating Result bits sixty-three through fifty-six. Source1 bits seventy-one through sixty-four are shifted by the number of bit positions in the shift count (Source2) generating Result bits seventy-one through sixty-four. Source1 bits seventy-nine through seventy-two are shifted by the number of bit positions in the shift count (Source2) generating Result bits seventy-nine through seventy-two. Source1 bits eighty-seven through eighty are shifted by the number of bit positions in the shift count (Source2) generating Result bits eighty-seven through eighty. Source1 bits ninety-five through eighty-eight are shifted by the number of bit positions in the shift count (Source2) generating Result bits ninety-five through eighty-eight. Source1 bits one hundred and three through ninety-six are shifted by the number of bit positions in the shift count (Source2) generating Result bits one hundred and three through ninety-six. Source1 bits one hundred and eleven through one hundred and four are shifted by the number of bit positions in the shift count (Source2) generating Result one hundred and eleven through one hundred and four. Source1 bits one hundred and nineteen through one hundred and twelve are shifted by the number of bit positions in the shift count (Source2) generating Result bits one hundred and nineteen through one hundred and twelve. Source1 bits one hundred and twenty-seven through one hundred and nineteen are shifted by the number of bit positions in the shift count (Source2) generating Result bits one hundred and twenty-seven through one hundred and nineteen.

[0162] In one embodiment, the shift count bits of Source2 are communicated to functional unit 203 by scaling or by translating in such a way as to enable either byte shifting or bit shifting of the Source1 data responsive to control signal 207. However, in an alternative embodiment, the bits of Source1 are communicated to functional unit 203 by multiplexing or by transposing in such a way as to enable either byte shifting or bit shifting responsive to control signal 207.

[0163] At processing block 733, the Result is stored in the DEST register.

[0164] Table 3 illustrates the in-register representation of packed shift right arithmetic operation. The first row of bits is the packed data representation of Source1. The second row of bits is the data representation of Source2. The third row of bits is the packed data representation of the Result. The number below each data element bit is the data element number. For example, Source1 data element three is 10000000₂. TABLE 3 00101010 01010101 01010101 11111111 10000000 01110000 10001111 10001000 Shift⁷ Shift⁶ Shift⁵ Shift⁴ Shift³ Shift² Shift¹ Shift⁰ 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000100 = = = = = = = = 00000010 00000101 00000101 11111111 11110000 00000111 11111000 11111000 7 6 5 4 3 2 1 0

[0165] Table 4 illustrates the in-register representation of packed shift right logical operation on packed byte data. TABLE 4 00101010 01010101 01010101 11111111 10000000 01110000 10001111 10001000 Shift⁷ Shift⁶ Shift⁵ Shift⁴ Shift³ Shift² Shift¹ Shift⁰ 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000011 = = = = = = = = 00000101 00001010 00001010 00011111 00010000 00001110 00010001 00010001 7 6 5 4 3 2 1 0

[0166] Table 5 illustrates the in-register representation of packed shift left logical operation on packed byte data. TABLE 5 00101010 01010101 01010101 11111111 10000000 01110000 10001111 10001000 Shift⁷ Shift⁶ Shift⁵ Shift⁴ Shift³ Shift² Shift¹ Shift⁰ 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000011 = = = = = = = = 01010000 10101000 10101000 11111000 00000000 10000000 01111000 01000000 7 6 5 4 3 2 1 0

[0167] Circuit Descriptions

[0168] The convention followed in the subsequent descriptions of circuits is that the bus names correspond to the signal names on that bus. For example, a Source1 signal is on a Source1 bus. Busses with multiple bits may be designated with particular bit ranges. For example, Source1[31:16] indicates that the bus corresponds to bits 31 through 16 of the Source1 bus. The whole bus may be referred to as the Source1 bus or Source1[63:0] (for a 64 bit bus). The complement of a signal may be referred to by appending an “#” after the signal name. For example, the complement of the Source1 signal on the Source1 bus is the Sourcel# signal on the Sourcel# bus.

[0169] Packed Shift Circuit

[0170] In one embodiment, the shift operation can occur on multiple data elements in the same number of clock cycles as a single shift operation on unpacked data. To achieve execution in the same number of clock cycles, parallelism is used. That is, registers are simultaneously instructed to perform the shift operation on the data elements. This is discussed in more detail below. FIG. 8 illustrates one embodiment of a portion of a circuit that can perform a shift operation on packed data in the same number of clock cycles as a shift operation on unpacked data.

[0171]FIG. 8 illustrates the use of a modified byte slice shift circuit, byte slice stage_(i) 899. Each byte slice, except for the most significant data element byte slice, includes a shift unit and bit control. The most significant data element byte slice need only have a shift unit.

[0172] Shift unit_(i) 811 and shift unit_(i+1) 871 each allow eight bits from Source1 to be shifted by the shift count. In one embodiment, each shift unit operates like a known eight bit shift circuit. Each shift unit has a Source1 input, a Source2 input, a control input, a next stage signal, a last stage signal, and a result output. Therefore, shift unit_(i) 811 has Source1_(i) 831 input, Source2[63:0] 833 input, control_(i) 801 input, next stage_(i) 813 signal, last stage_(i) 812 input, and a result stored in result register_(i) 851. Therefore, shift unit_(i+1) 871 has Source1_(i+1) 832 input, Source2[63:0] 833 input, control_(i+1) 802 input, next stage_(i+1) 873 signal, last stage_(i+1) 872 input, and a result stored in result register_(i+1) 852.

[0173] The Source1 input is typically an eight bit portion of Source1. The eight bits represents the smallest type of data element, one packed byte data element. Source2 input represents the shift count. In one embodiment, each shift unit receives the same shift count from Source2[63:0] 833. Operation control 800 transmits control signals to enable each shift unit to perform the required shift. The control signals are determined from the type of shift (arithmetic/logical) and the direction of the shift. The next stage signal is received from the bit control for that shift unit. The shift unit will shift the most significant bit out/in on the next stage signal, depending on the direction of the shift (left/right). Similarly, each shift unit will shift the least significant bit out/in on the last stage signal, depending on the direction of the shift (right/left). The last stage signal being received from the bit control unit of the previous stage. The result output represents the result of the shift operation on the portion of Source1 the shift unit is operating upon.

[0174] Bit control_(i) 820 is enabled from operation control 800 via packed data enable_(i) 806. Bit control_(i) 820 controls next stage_(i) 813 and last stage_(i+1) 872. Assume, for example, shift unit_(i) 811 is responsible for the eight least significant bits of Source1, and shift unit_(i+1) 871 is responsible for the next eight bits of Source1. If a shift on packed bytes is performed, bit control_(i) 820 will not allow the least significant bit from shift unit_(i+1) 871 to be communicated with the most significant bit of shift unit_(i) 811. However, a shift on packed words is performed, then bit control_(i) 820 will allow the least significant bit from shift unit_(i+1) 871 to be communicated with the most significant bit of shift unit_(i) 811 For example, in Table 6, a packed byte arithmetic shift right is performed. Assume that shift unit_(i+1) 871 operates on data element one, and shift unit_(i) 811 operates on data element zero. Shift unit_(i+1) 871 shifts its least significant bit out. However operation control 800 will cause bit control_(i) 820 to stop the propagation of that bit, received from last stage_(i+1) 821, to next stage_(i) 813. Instead, shift unit_(i) 811 will fill the high order bits with the sign bit, Source1[7]. TABLE 6 . . . . . . . . . . . . . . . . . . 00001110 10001000 Shift⁷ Shift⁶ Shift⁵ Shift⁴ Shift³ Shift² Shift¹ Shift⁰ . . . . . . . . . . . . . . . . . . . . . 00000001 = = = = = = = = . . . . . . . . . . . . . . . . . . 00001111 11000100 7 6 5 4 3 2 1 0

[0175] However, if a packed word arithmetic shift is performed, then the least significant bit of shift unit_(i+1) 871 will be communicated to the most significant bit of shift unit_(i) 811. Table 7 illustrates this result. This communication would be allowed for packed doubleword shifts as well. TABLE 7 . . . . . . . . . 00001110 10001000 Shift³ Shift² Shift¹ Shift⁰ . . . . . . . . . 00000001 = = = = . . . . . . . . . 00000111 01000100 3 2 1 0

[0176] Each shift unit is optionally connected to a result register. The result register temporarily stores the result of the shift operation until the complete result, Result[63:0] 860 can be transmitted to the DEST register.

[0177] For a complete sixty-four bit packed shift circuit, eight shift units and seven bit control units are used. Such a circuit can also be used to perform a shift on a sixty-four bit unpacked data, thereby using the same circuit to perform the unpacked shift operation and the packed shift operation.

[0178] Another Packed Shift Circuit

[0179]FIG. 9 illustrates another embodiment of a packed shift circuit. In one embodiment, the packed shift circuit is capable of performing arithmetic shift operations on multiple data types. For example, the packed shift circuit may be capable of performing a packed shift on data elements which each contain one 64-bit value, two 32-bit data values, or four 16-bit values. This embodiment may also be implemented to be capable of alternatively or additionally performing logical shift operations, right shifts, and/or left shifts.

[0180] A barrel shifter 905 is used to shift Source1 by the count specified in the low order bits of Source2. However, if Source1 is a packed data type, the barrel shifter shifts the low order bits of each of the values in the packed data type into the high order bits of the next lowest order value to produce a shifted packed intermediate result. A correction circuit is used to replace each of these bits with the most significant bit of the corresponding value if it is a signed shift operation, and a zero if it is a logical shift operation. In one embodiment, if at least one of the high order bits that are not required to specify the shift count is one, all the bits of the shifted packed intermediate result are replaced with the sign bit (for right arithmetic shifts) or zero (for logical shifts). One embodiment of the barrel shifter 905 is described with reference to FIG. 10.

[0181] The shift data is driven on a Source1 bus 901. The shift count is driven on a Source2 bus 902 in two portions, Source2[5:0], an actual shift count bus 903, Source2[63:6], and an overflow shift count bus 904. The six bits required to specify a shift count ranging from 0 to 63 are specified on the actual shift count bus 903. The rest of the 64-bit data field is specified on the overflow shift count bus 904. The Source1 bus 901, the actual shift count bus 903, and a left shift bus 900 are coupled to the inputs of the barrel shifter 905. In one embodiment, the barrel shifter 905 contains a set of muxes that use complex gates (described below) to drive a set of 16-1 muxes which form one stage of the barrel shifter 905. The barrel shifter 905 drives a shift output bus 919.

[0182] Muxes 906-909 drive the replacements bits that are used to correct the appropriate bits of a shift output bus 914. Each of the muxes 906-909 corresponding to the most-significant to the least significant word of the shift output bus 914, respectively. A right-shift arithmetic doubleword (rsadword) bus 928 is coupled to the most-significant select bit of each of the muxes 906-909 to indicate whether the shift operation is an arithmetic right shift that operated on packed doubleword data. A right-shift arithmetic word (rsaword) bus 929 is coupled to the least-significant select bit of each of the muxes 906-909 to indicate whether the shift operation is an arithmetic right shift that operated on packed word data. The rsadword signal and the rsaword signal may be generated based on the decoding of the control signal 207, for example. A zero is driven through a set of zero busses 924-927 which are coupled to the zero input of each of the muxes 906-909, respectively. A zero is used to correct the selected bits on the shift output bus 919 when the operation is neither a right shift arithmetic word or right shift arithmetic doubleword operation. The operation may be a left shift or a logical shift, for example. When the operation is a rsaword operation, the most significant bit of each word (the sign bit) is used to correct the selected bit of each corresponding word of the shifted packed intermediate result on the shift output bus 919. A Source1[63] bus 920, a Source1[47] bus 921, a Source1[31] bus 922, and a Source1[15] bus 923 are coupled to the corresponding 1 inputs of each of the muxes 906-909, respectively. The sign bit of each of the words of the packed word data are driven onto the corresponding bus. When the operation is a rsadword operation, the most significant bit of each doubleword (the sign bit) is used to correct the selected bits of each corresponding doubleword of the shifted packed intermediate result on the shift output bus 919. The Source1[63] bus 920 and the Source1[31] bus 922 are coupled to the corresponding two inputs of muxes 906-907 and muxes 908-909, respectively. The sign bit of each of the corresponding doublewords is driven onto the corresponding bus. Each of the muxes 906-909 drives a corresponding replacement bit bus 996-999.

[0183] The actual shift count bus 903 is also coupled to the input of a less-than-or-equal-to (<=) decoder logic 930 which drives a 64-bit decoded signal on the decoded bus 938. The decoded signal is a field of zeroes with ones in the bit positions corresponding to numbers less than or equal to the value on the actual shift count bus 903. The bits that are one correspond to the bit positions of the shift output bus that should be corrected if the operation were a left shift of a 64-bit scalar data. The value on the decoded bus 938 is received and manipulated by a fixshift circuit 932 to produce the values on the fixdata busses 934-937 according to the operation and data type specified on the control bus 933 such that the appropriate bits of each value of the shifted packed intermediate result are corrected. For example, if a right shift of packed word data were indicated on the control bus 933 and a shift count of 6 was indicated on the actual shift count bus 903, the fixshift circuit 932 would replicate the least-significant 6 ones produced on the 64-bit decoded bus 938 on the most-significant 6 bits of each of the 16-bit fixdata busses 934-937. Alternatively, if a left shift of packed word data were indicated on the control bus 933 and a shift count of 6 was indicated on the actual shift count bus 903, the fixshift circuit 932 would replicate the least-significant 6 ones produced on the 64-bit decoded bus 938 on the least-significant 6 bits of each of the 16-bit fixdata busses 934-937. The the overflow shift count bus 904 is input to NOR logic 931 which produces an output on the NOR bus 939 that is one only if all the bits of the Source2[63:6] bus 904 are zero. When the NOR bus 939 is low, the Fixshift circuit 932 indicates that all bits should be replaced. More details of the Fixshift circuit 932 is provided below.

[0184] Each of the bits of the most significant word of the shift output bus 919 (S_(O)[63:48]) are coupled to the zero input of a corresponding one of the set of muxes 910. The replacement bit bus 996 which corresponds to the replacement bit for the most significant word is coupled to the one input of each of the set of muxes 910. Each bit of the fixdata bus 934 is coupled to the corresponding one of the set of muxes 910 to indicate whether the corresponding bit of the S_(O)[63:48] data or the corresponding bit on the replacement bit bus 996 is driven onto a corresponding bit of the fixed shift output (FS_(O)[63:48]) bus. The inputs and outputs of muxes 911-913 are similarly coupled, as illustrated in FIG. 9.

[0185] While FIG. 9 illustrates one circuit for implementation of a shifter circuit, any number of well-known shifter circuits providing the equivalent function may be used.

[0186] Fixshift Circuit

[0187]FIG. 10 illustrates one embodiment of the fixshift circuit 932. The control bus 933 comprises a left-shift word (lsw) bus 1000, a right-shift word doubleword (rswd) bus 1001, a left-shift doubleword quadword (lsdq) bus 1002, a left-shift word doubleword quadword (lswdq) bus 1003, a right-shift word (rsw) bus 1004, a right-shift doubleword (rsd) bus 1005, a right-shift quadword (rsq) bus 1006, a left-shift doubleword (lsd) bus 1007, a right-shift word doubleword quadword (rswdq) bus 1008, a left-shift word doubleword (lswd) bus 1009, a right-shift doubleword quadword (rsdq) bus 1010, and a left-shift quadword (lsq) bus 1011. These signals may be generated based on the decoding of the control signal 207, for example. The names of the individual control signals indicate when they are asserted (active). These signals are a one when they are active (active high). For example, the lsw bus 1000 is only active when the operation is a left-shift of a packed word data. The rswd bus 1001 is only active when the operation is a right-shift operation of a packed word data or a packed doubleword data. Each of the busses of the control bus 933 are coupled to a corresponding one of inverters 1020-1031 which drive one of the corresponding busses comprising an lsw# bus 1040, an rswd# bus 1041, an lsdq# bus 1042, an lswdq# bus 1043, an rsw# bus 1044, an rsd# bus 1045, an rsq# bus 1046, an lsd# bus 1047, an rswdq# bus 1048, an lswd# bus 1049, an rsdq# bus 1050, and an lsq# bus 1051, respectively. These signals are zero when they are active (active low).

[0188] Each of a set of muxes 1060 drives a bit of the fixdata bus 937 to indicate which bits of the least significant word of the shift output bus 919 (referring to FIG. 9) should be replaced. The lswdq# bus 1043 is coupled to the select 0 input of each of the set of muxes 1060 to select each data 0 input whenever the operation is a left-shift of either a word, doubleword, or quadword. Each bit of the least significant word of the decoded bus 938 is coupled to a corresponding data input 0 of each of the set of muxes 1060. For example, the three least significant bits of the fixdata bus 937 would indicate that the three least significant bits of the least significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a lswdq with a shift count of 3. The rsw# bus 1044 is coupled to the select 1 input of each of the set of muxes 1060 to select each data 1 input whenever the operation is a right-shift of a word. Each bit of the least significant word of the decoded bus 938 is coupled to a corresponding data input 1 of each of the set of muxes 1060 in reverse order (The most significant bit of the decoded bus 938 drives the one of the set of muxes 1060 that drives the least significant bit of the fixdata bus 937, the second most significant bit of the decoded bus 938 drives the one of the set of muxes 1060 that drives the second least significant bit of the fixdata bus 937, etc.). For example, the three most significant bits of the fixdata bus 937 would indicate that the three least significant bits of the least significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a rsw with a shift count of 3. The rsd# bus 1045 is coupled to the select 2 input of each of the set of muxes 1060 to select each data 2 input whenever the operation is a right-shift of a doubleword. Each bit of the second least significant word of the decoded bus 938 is coupled to a corresponding data input 2 of each of the set of muxes 1060 in reverse order. For example, the three most significant bits of the fixdata bus 937 would indicate that the three least significant bits of the least significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a rsd with a shift count of 19. The right shift shifts through the most significant word of the least significant doubleword before it begins to effect the least significant word. The rsq# bus 1046 is coupled to the select 3 input of each of the set of muxes 1060 to select each data 3 input whenever the operation is a right-shift of a quadword. Each bit of the most significant word of the decoded bus 938 is coupled to a corresponding data input 3 of each of the set of muxes 1060 in reverse order. For example, the three most significant bits of the fixdata bus 937 would indicate that the three least significant bits of the least significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a rsq with a shift count of 51. The right shift shifts through the most significant 48 bits of the quadword before it begins to effect the least significant word.

[0189] The lswdq bus 1003, the rsw bus 1004, the rsd bus 1005, and the rsq bus 1006 are coupled to a NOR gate 1013 which drives a zero bus 1017. The zero bus 1017 is coupled to the control 0 (c0) input of each of the set of muxes 1060 to force a zero on all the bits of the fixdata bus 937 when none of the select inputs are active. In addition the NOR bus 939 is coupled to the control 1 (c1) input of each of the muxes to force a one on all the bits of the fixdata bus 937 when at least one of the most-significant bits on the overflow shift count bus 904 is non-zero. This forces all the bits of the shifted packed intermediate result on the shift output bus 719 to be replaced. This produces a result that is consistent with a Source1 value that is extended beyond the most significant and least significant bits of the register. If such a value is shifted by greater than the register size, the sign bit (for right arithmetic shifts) or the zero bits (for logical shifts) should replace the whole field.

[0190] Each of a set of muxes 1061 drives a bit of the fixdata bus 936 to indicate which bits of the second least significant word of the shift output bus 919 (referring to FIG. 9) should be replaced. The lsw# bus 1040 is coupled to the select 0 input of each of the set of muxes 1061 to select each data 0 input whenever the operation is a left-shift of a word. Each bit of the least significant word of the decoded bus 938 is coupled to a corresponding data input 0 of each of the set of muxes 1061. For example, the three least significant bits of the fixdata bus 936 would indicate that the three least significant bits of the second least significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a lsw with a shift count of 3. The rswd# bus 1041 is coupled to the select 1 input of each of the set of muxes 1061 to select each data 1 input whenever the operation is a right-shift of a word or a doubleword. Each bit of the least significant word of the decoded bus 938 is coupled to a corresponding data input 1 of each of the set of muxes 1061 in reverse order. For example, the three most significant bits of the fixdata bus 936 would indicate that the three least significant bits of the second least significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a rswd with a shift count of 3. The Isdq# bus 1042 is coupled to the select 2 input of each of the set of muxes 1061 to select each data 2 input whenever the operation is a left-shift of a doubleword or a quadword. Each bit of the second least significant word of the decoded bus 938 is coupled to a corresponding data input 2 of each of the set of muxes 1061. For example, the three least significant bits of the fixdata bus 936 would indicate that the three least significant bits of the second least significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a lsdq with a shift count of 19. The left shift shifts through the least significant word before it begins to effect the second least significant word. The rsq# bus 1046 is coupled to the select 3 input of each of the set of muxes 1061 to select each data 3 input whenever the operation is a right-shift of a quadword. Each bit of the second most significant word of the decoded bus 938 is coupled to a corresponding data input 3 of each of the set of muxes 1061 in reverse order. For example, the three most significant bits of the fixdata bus 936 would indicate that the three least significant bits of the second least significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a rsq with a shift count of 35. The right shift shifts through the most significant doubleword of the quadword before it begins to effect the second least significant word.

[0191] The lsw bus 1000, the rswd bus 1001, the lsdq bus 1002, and the rsq bus 1006 are coupled to a NOR gate 1012 which drives a zero bus 1016. The zero bus 1016 is coupled to the control 0 (c0) input of each of the set of muxes 1061 to force a zero on all the bits of the fixdata bus 936 when none of the select inputs are active. In addition the NOR bus 939 is coupled to the control 1 (c1) input of each of the muxes to force a one on all the bits of the fixdata bus 936 when at least one of the most-significant bits on the overflow shift count bus 904 is non-zero. This forces all the bits of the shifted packed intermediate result on the shift output bus 719 to be replaced.

[0192] Each of a set of muxes 1062 drives a bit of the fixdata bus 935 to indicate which bits of the second most significant word of the shift output bus 919 (referring to FIG. 9) should be replaced. The lswd# bus 1049 is coupled to the select 0 input of each of the set of muxes 1062 to select each data 0 input whenever the operation is a left-shift of either a word or doubleword. Each bit of the least significant word of the decoded bus 938 is coupled to a corresponding data input 0 of each of the set of muxes 1062. For example, the three least significant bits of the fixdata bus 935 would indicate that the three least significant bits of the second most significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a lswd with a shift count of 3. The rsw# bus 1044 is coupled to the select 1 input of each of the set of muxes 1062 to select each data 1 input whenever the operation is a right-shift of a word. Each bit of the least significant word of the decoded bus 938 is coupled to a corresponding data input 1 of each of the set of muxes 1060 in reverse order. For example, the three most significant bits of the fixdata bus 935 would indicate that the three least significant bits of the second most significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a rswd with a shift count of 3. The rsdq# bus 1050 is coupled to the select 2 input of each of the set of muxes 1062 to select each data 2 input whenever the operation is a right-shift of a doubleword or quadword. Each bit of the second least significant word of the decoded bus 938 is coupled to a corresponding data input 2 of each of the set of muxes 1062 in reverse order. For example, the three most significant bits of the fixdata bus 935 would indicate that the three least significant bits of the second most significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a rsdq with a shift count of 19. The right shift shifts through the most significant word before it begins to effect the second least significant word. The lsq# bus 1051 is coupled to the select 3 input of each of the set of muxes 1062 to select each data 3 input whenever the operation is a left-shift of a quadword. Each bit of the second most significant word of the decoded bus 938 is coupled to a corresponding data input 3 of each of the set of muxes 1062 in reverse order. For example, the three most significant bits of the fixdata bus 935 would indicate that the three least significant bits of the second most significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a lsq with a shift count of 35. The left shift shifts through the least significant doubleword before it begins to effect the second most significant word.

[0193] The lsw bus 1000, the rsw bus 1004, the rsdq bus 1010, and the lsq bus 1011 are coupled to a NOR gate 1014 which drives a zero bus 1018. The zero bus 1018 is coupled to the control 0 (c0) input of each of the set of muxes 1062 to force a zero on all the bits of the fixdata bus 935 when none of the select inputs are active. In addition the NOR bus 939 is coupled to the control 1 (c1) input of each of the muxes to force a one on all the bits of the fixdata bus 935 when at least one of the most-significant bits on the overflow shift count bus 904 is non-zero. This forces all the bits of the shifted packed intermediate result on the shift output bus 719 to be replaced.

[0194] Each of a set of muxes 1063 drives a bit of the fixdata bus 934 to indicate which bits of the most significant word of the shift output bus 919 (referring to FIG. 9) should be replaced. The lsw# bus 1000 is coupled to the select 0 input of each of the set of muxes 1063 to select each data 0 input whenever the operation is a left-shift of a word. Each bit of the least significant word of the decoded bus 938 is coupled to a corresponding data input 0 of each of the set of muxes 1063. For example, the three least significant bits of the fixdata bus 934 would indicate that the three least significant bits of the most significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a lsw with a shift count of 3. The lsd# bus 1047 is coupled to the select 1 input of each of the set of muxes 1063 to select each data 1 input whenever the operation is a left-shift of a doubleword. Each bit of the least significant word of the decoded bus 938 is coupled to a corresponding data input 1 of each of the set of muxes 1063. For example, the three least significant bits of the fixdata bus 934 would indicate that the three least significant bits of the most significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a lsd with a shift count of 19. The left shift shifts through the second least significant word before it begins to effect the most significant word. The rswdq# bus 1048 is coupled to the select 2 input of each of the set of muxes 1063 to select each data 2 input whenever the operation is a right-shift of a word, doubleword, or quadword. Each bit of the least significant word of the decoded bus 938 is coupled to a corresponding data input 2 of each of the set of muxes 1063 in reverse order. For example, the three most significant bits of the fixdata bus 934 would indicate that the three least significant bits of the most significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a rswdq with a shift count of 3. The lsq# bus 1045 is coupled to the select 3 input of each of the set of muxes 1063 to select each data 3 input whenever the operation is a left-shift of a quadword. Each bit of the most significant word of the decoded bus 938 is coupled to a corresponding data input 3 of each of the set of muxes 1060. For example, the three most significant bits of the fixdata bus 934 would indicate that the three least significant bits of the most significant word of the shift output bus 919 (referring to FIG. 9) should be replaced for a lsq with a shift count of 51. The left shift shifts through the least significant 48 bits of the quadword before it begins to effect the most significant word.

[0195] The lsw bus 1000, the lsd bus 1007, the rswdq bus 1008, and the lsq bus 1011 are coupled to a NOR gate 1015 which drives a zero bus 1019. The zero bus 1019 is coupled to the control 0 (c0) input of each of the set of muxes 1063 to force a zero on all the bits of the fixdata bus 934 when none of the select inputs are active. In addition the NOR bus 939 is coupled to the control 1 (c1) input of each of the muxes to force a one on all the bits of the fixdata bus 934 when at least one of the most-significant bits on the overflow shift count bus 904 is non-zero. This forces all the bits of the shifted packed intermediate result on the shift output bus 719 to be replaced.

[0196] While FIG. 10 illustrates one circuit for implementation of the fixshift circuit 932 of FIG. 9, it will be appreciated that any number of alternative fixshift circuits could be used in combination with or not in combination with a sequence of machine executable emulation instructions.

[0197] Barrel Shifter

[0198]FIG. 11 illustrates one embodiment of the barrel shifter 905 (referring to FIG. 9). The barrel shifter 905 is implemented to perform right shifts. In order to perform left shifts, a right shift of the two's complement of the right shift count is performed according to well-known methods. The actual shift count bus 903 comprises an Source2[0] bus 1100, an Source2[1] bus 1101, an Source2[2] bus 1102, an Source2[3] bus 1103, an Source2[4] bus 1104, and an Source2[5] bus 1105. The Source2[1] bus 1101 and the shift left bus 900 are coupled to logic 1110 which generates a signal on select bus 1120 that is the value of Source2[1] when the operation is a right shift and the complement of Source2[1] when the operation is a left shift. The select bus 1120 is coupled to the select input of a set of 2-1 Muxes 1140. The Source1[63:0] bus 901 is coupled to circuit 1161 which replicates the 64-bit data to produce a 128-bit data (where one copy of the 64-bit data is in the most significant quadword and the other is in the least significant quadword) on the data[127:0] bus 1130. In one embodiment, the circuit 1161 is simply wires that branch each single bit input to two output bits at the appropriate bit positions. Each bit of the data[127:2] portion of the data[127:0] bus 1130 is coupled to each corresponding 1 input of the set of 2-1 Muxes 1140. Each bit of the data[125:0] portion of the data[127:0] bus 1130 is coupled to each corresponding 0 input of the set of 2-1 Muxes 1140. The set of 2-1 Muxes 1140 are coupled to corresponding bits of an intermediate result bus 1141. When the select bus 1120 is driven high, data [127:2] is driven onto the intermediate result bus 1141 thereby shifting the data by two positions. When the select bus 1120 is driven low, data[125:0] is driven onto the intermediate result bus 1141.

[0199] The next stage of the barrel shifter 905 shifts the data on the intermediate result bus 1141 by 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, or 60 positions depending on the value of the bits on the Source2[2] bus 1102, the Source2[3] bus 1103, the Source2[4] bus 1104 and the Source2[5] bus 1105. The Source2[2] bus 1102 is coupled to logic 1111 (described in more detail below) which drives the two bits of the bitpair bus 1121. The first bit is Source2[2] when the operation is a right shift and the complement of Source2[2] when the operation is a left shift. The second bit is the complement of the first bit. The Source2[3] bus 1103, the Source2[4] bus 1104, and the Source2[5] bus 1105 are coupled to logic circuits 1112-1114, respectively, which drive bitpair busses 1122-1124, respectively, in a similar manner. The bitpair busses 1121-1124 are coupled to the inputs of decoder 1116 that generates a decoded value of the bitpair busses 1121-1124 on the select bus 1162 according to well-known methods. Each bit of the intermediate result [65:0] portion of the intermediate result bus 1141 is coupled to the 0 inputs of the corresponding one of the set of 16-1 Muxes 1150. Each bit of the intermediate result [69:4] portion of the intermediate result bus 1141 is coupled to the 1 inputs of the corresponding one of the set of 16-1 Muxes 1150. Each bit of the intermediate result [125:60] portion of the intermediate result bus 1141 is coupled to the 15 inputs of the corresponding one of the set of 16-1 Muxes 1150. The 2 inputs through the 14 inputs are coupled in a manner according to the pattern illustrated in FIG. 11 and described above. The set of muxes 1150 drive an intermediate result bus 1151 according to the input selected by the decoded value on the select bus 1162.

[0200] The last stage of the barrel shifter 905 shifts the data on the intermediate result bus 1151 by 0, 1, or 2 positions according to the value on the Source2[0] bus 1100 and the shift left bus 900. The Source2[0] bus 1100 and the shift left bus 900 are coupled to the inputs of a logic circuit 1115 which drives the select bus 1125. The logic circuit 1115 adds the values of the bits on the Source2[0] bus 1100 and the shift left bus 900 and drives the decoded sum on the select bus 1125 according to well-known methods. The select bus 1125 is coupled to a set of 3-1 Muxes 1160. Each bit of the intermediate result [63: 0] portion of the intermediate result bus 1151 is coupled to the 0 inputs of the corresponding one of the set of 3-1 Muxes 1160. Each bit of the intermediate result [64: 1] portion of the intermediate result bus 1151 is coupled to the 1 inputs of the corresponding one of the set of 3-1 Muxes 1160. Each bit of the intermediate result [65: 2] portion of the intermediate result bus 1151 is coupled to the 2 inputs of the corresponding one of the set of 3-1 Muxes 1160. Each of the set of 3-1 Muxes 1160 drives the corresponding bit of the result on the shifted output bus 919 according to the input selected by the decoded sum on the select bus 1125.

[0201] While FIG. 10 illustrates one circuit for implementation of the fixshift circuit 932 of FIG. 8, any number of alternative fixshift circuits could be used.

[0202] Encoding Logic

[0203]FIG. 12 illustrates one embodiment of the encoding logic represented in FIG. 11 as each of the logic circuits 1111-1114. A shift count bit is driven onto the S bus 1220 (which corresponds to each of the first bit of a bitpair bus as described above) and the complement of the shift count bit is driven onto the S# bus (which corresponds to the second bit of a bitpair bus as described above) when the shift left bus 1203 indicates that the operation is a right shift. The complement of the shift count bit is driven onto the S bus 1220 and the shift count bit is driven onto the S# bus when the shift left bus 1203 indicates that the operation is a left shift.

[0204] The shift count bit is driven on a shiftcount bit bus 1202 which is coupled to the input of an inverter 1210. Inverter 1210 drives the complement of the shift count bit on the shiftcount bit# bus 1204 which is coupled to the input of an inverter 1212. Inverter 1212 drives the bit to be encoded on a delayed shiftcount bit bus 1206. The shift left bus 1203 is coupled to the input of inverter 1211 which drives the complement of the shift left signal on the shift left# bus 1205. The shift left# bus 1205 is coupled to an inverter 1213 which drives the delayed shift left bus 1207.

[0205] The shiftcount bit# bus 1204 is coupled to the first input of complex gate 1214 and the fourth input of complex gate 1215. The delayed shiftcount bus 1206 is coupled to the fourth input of complex gate 1214 and the second input of complex gate 1215. The shift left# bus 1205 is coupled to the third input of complex gate 1214 and the third input of complex gate 1215. The delayed shift left bus 1207 is coupled to the first input of complex gate 1214 and the first input of complex gate 1215.

[0206] Table 8 is the truth table for both complex gate 1214 and complex gate 1215. The output is false whenever either the first two inputs are true or the second two inputs are true. Otherwise, the output is false. The implementation of this logic as a complex gate improves performance. This is particularly important since the logic decodes 4 bits for the second stage of this 64-bit barrel shifter as compared to 3 bits for the second stage in a 32-bit barrel shifter. TABLE 8 Complex Gate Truth Table First Second Third Fourth Input Input Input Input OUT 0 0 0 0 1 0 0 0 1 1 0 0 1 0 1 0 0 1 1 0 0 1 0 0 1 0 1 0 1 1 0 1 1 0 1 0 1 1 1 0 1 0 0 0 1 1 0 0 1 1 1 0 1 0 1 1 0 1 1 0 1 1 0 0 0 1 1 0 1 0 1 1 1 0 0 1 1 1 1 0

[0207] Method of Performing A Packed Shift Operation

[0208]FIG. 13 illustrates one embodiment of a method of performing a Packed Shift Operation.

[0209] In Processing block 1301, a first packed data is accessed from a register or another memory, such as RAM, a cache memory, a flash memory, or other data storage device. The first packed data represents multiple values to be shifted.

[0210] In Processing block 1302, a shift count is accessed from a register or another memory. The shift count represents the number of positions each value of the first packed data is to be shifted.

[0211] In Processing block 1303, the first packed data is shifted by the number of positions indicated by the shift count to produce an shifted packed intermediate result. In one embodiment, portions of some values of the shifted packed intermediate result may be shifted into other values of the shifted packed intermediate result.

[0212] In Processing block 1305, the correction circuit determines whether the shift count is greater than the number of bits to be shifted in the first packed data. If so, Processing block 1306 is performed. If not Processing block 1307 is performed.

[0213] In Processing block 1306, all the bits of the shifted packed intermediate data is replaced by the corresponding replacement bit. This produces a result that is consistent with a first packed data having values that are extended beyond the most significant and least significant bits represented. If such a value is shifted by greater than the number of bits represented, the sign bit (for right arithmetic shifts) or the zero bits (for logical shifts) should replace the whole value.

[0214] In Processing block 1307, at least one bit of the shifted packed intermediate data is replaced by the corresponding replacement bit. In one embodiment, the replacement bits correspond to those bits in those portions of the values of the shifted packed intermediate result that are shifted into other values of the shifted packed intermediate result.

[0215] Alternative Shift Circuits

[0216]FIG. 14a illustrates one alternative embodiment of a packed shift circuit that provides for shifting one hundred and twenty-eight bit packed data. Barrel shifter 1405 comprises circuit 1460, shifter multiplexers (MUXes) 1440, and shift control 1410. In a manner similar to that previously described for sixty-four bit packed data, circuit 1460 receives Source1 bits one hundred and twenty-seven through zero, and produces two hundred and fifty-six bits as input to shifter MUXes 1440. Shift control 1410 receives a Left Shift signal and Source2 bits six through zero and directs shifter MUXes 1440 to perform effective right or left shifts of Source1. Correction circuit 1490 receives data inputs from barrel shifter 1405 and generates correction data in accordance with the shift operation being performed, the Left Shift signal and the value of Source2, producing as output Result bits one hundred and twenty-seven through zero.

[0217] One embodiment of the packed shifter circuit of FIG. 14a provides for shifting of packed bytes by as many as eight bit positions, packed words by as many as sixteen bit positions, packed doublewords by as many as thirty-two bit positions, packed quadwords by as many as sixty-four bit positions, and doublewords by as many as one hundred and twenty-eight bit positions.

[0218]FIG. 14b illustrates another alternative embodiment of a Packed Shift circuit that provides for shifting one hundred and twenty-eight bit packed data. The circuit comprises two identical sixty-four bit shifters with a structure similar to that previously described in FIG. 9, FIG. 10 and FIG. 11. Each barrel shifter 905 comprises circuit 1461, shifter multiplexers (MUXes) 1441, and shift control 1411. In the most significant barrel shifter 905, the most significant circuit 1461 receives Source1 bits one hundred and twenty-seven through sixty-four, and produces one hundred and twenty-eight bits as input to the most significant shifter MUXes 1441. In the least significant barrel shifter 905, the least significant circuit 1461 receives Source1 bits sixty-three through zero, and produces one hundred and twenty-eight bits as input to the least significant shifter MUXes 1441.

[0219] Shift control 1410 of the both the most significant barrel shifter 905 and the least significant barrel shifter 905 receive a Left Shift signal and Source2 bits five through zero and directs their corresponding shifter MUXes 1441 to perform effective right or left shifts on their respective quadword of Source1.

[0220] The most significant correction circuit 1491 receives data inputs from the most significant barrel shifter 905 and generates correction data in accordance with the shift operation being performed, the Left Shift signal and the value of Source2, producing as output Result bits one hundred and twenty-seven through sixty-four. The least significant correction circuit 1491 receives data inputs from the least significant barrel shifter 905 and generates correction data in accordance with the shift operation being performed, the Left Shift signal and the value of Source2, producing as output Result bits sixty-three through zero.

[0221] One embodiment of the packed shift circuit of FIG. 14b provides for shifting of packed bytes by as many as eight bit positions, packed words by as many as sixteen bit positions, packed doublewords by as many as thirty-two bit positions, and packed quadwords by as many as sixty-four bit positions. It will be appreciated that for certain embodiments, the packed shift circuit of FIG. 14b may be realized more efficiently than the packed shift circuit of FIG. 14a, providing in some cases for reduced circuitry, area and cost. It will also be appreciated that for certain embodiments, the packed shift circuit of FIG. 14b may in some cases produce results in less time than the packed shift circuit of FIG. 14a. But it will also be appreciated that one embodiment of the packed shift circuit of FIG. 14a may provide for additional functionality in comparison to the functionality provided by the packed shift circuit of FIG. 14b. In some cases it may be desirable to also provide for this additional functionality.

[0222] Alignment Operations

[0223] Due to the nature of mixed media data manipulation, algorithms often include processing groups of bytes or words. As the size of a register is increased to one hundred and twenty-eight bits or more, it is increasingly more likely for a group of bytes or words in memory to be misaligned with the register, or with another packed data stored in another register or in memory. In such cases it is desirable to provide instructions for easily aligning packed data. The packed shift circuit of FIG. 14a provides for alignment shifting since it is possible to shift a packed data element from one position in a register to any other position in the register by performing a doubleword shift by as many as one hundred and twenty-eight bit positions.

[0224] One embodiment of processor 109 may provide alignment hardware to automatically align a packed data stored at a memory location having an arbitrary byte address with the least significant byte of a register as the packed data is being loaded from the memory location into the register. But, this type of automatic alignment is provided at additional cost and may cause undesirable delays for a majority of memory operations. It will be appreciated that while one embodiment of the packed shift circuit of FIG. 14a provides for alignment shifting, the Source2 count is used to shift the packed data by bit positions. It may be desirable in alignment shifting to shift the packed data by a number of positions that are not pit positions. For example, to align memory addresses in a typical byte addressable memory scheme, it is desirable to provide alignment shifting by byte positions, thus avoiding a step of converting a byte position count to a bit position count.

[0225] For one embodiment of the packed shift circuit of FIG. 14a, shift control 1410 provides for scaling of Source2 by multiplexing Source2 bits six through zero and Source2 bits nine through three to selectively use Source2 respectively as a bit position count or a byte position count in accordance with the desired operation.

[0226] On the other hand, it is also possible to modify the packed shift circuit of FIG. 14b to provide byte alignment shifting. FIG. 15 illustrates one embodiment of a circuit for allowing byte alignment with a Packed Shift circuit. Prior to providing Source1 as input to circuit 1461, the bits of Source1 may be transposed to generate a new packed data source, Source1′ (read “source-one-prime”) by circuit 1501. In circuit 1501, the value of Source1′ bit zero is taken directly from the value of Source1 bit zero. The value of Source1′ bit one is selected by multiplexer 1521 either from the value of Source1 bit one if byte-shift select 1511 is zero or from Source1 bit eight if byte-shift select 1511 is one. The value of Source1′ bit two is selected by multiplexer 1522 either from the value of Source1 bit two if byte-shift select 1511 is zero or from Source1 bit sixteen if byte-shift select 1511 is one. The value of Source1′ bit three is selected by multiplexer 1523 either from the value of Source1 bit three if byte-shift select 1511 is zero or from Source1 bit twenty-four if byte-shift select 1511 is one. Source1′ bits four through fifteen are similarly selected according to the value of byte-shift select 1511.

[0227] The value of Source1′ bit sixteen is selected by multiplexer 1536 either from the value of Source1 bit sixteen if byte-shift select 1511 is zero or from Source1 bit one if byte-shift select 1511 is one. The value of Source1′ bit seventeen is selected by multiplexer 1521 either from the value of Source1 bit seventeen if byte-shift select 1511 is zero or from Source1 bit nine if byte-shift select 1511 is one. Source1′ bits eighteen through one hundred and twenty-seven are similarly selected according to the value of byte-shift select 1511.

[0228] In other words, the value of Source1′ bit i is selected by a multiplexer either from the value of Source1 bit i if byte-shift select 1511 is zero or from Source1 bit j if byte-shift select 1511 is one, where j=8*(i MOD 16)+(i DIV 16).

[0229] Prior to storing Result produced by correction circuit 1491 into a destination register DEST, the bits of Result may be inversely transposed to generate a new packed data by circuit 1502. In circuit 1502, the value of DEST bit zero is taken directly from the value of Result bit zero. The value of DEST bit one is selected by multiplexer 1551 either from the value of Result bit one if byte-shift select 1512 is zero or from Result bit sixteen if byte-shift select 1512 is one. The value of DEST bit two is selected by multiplexer 1552 either from the value of Result bit two if byte-shift select 1512 is zero or from Result bit thirty-two if byte-shift select 1512 is one. DEST bits three through seven are similarly selected according to the value of byte-shift select 1512.

[0230] The value of DEST bit eight is selected by multiplexer 1558 either from the value of Result bit eight if byte-shift select 1512 is zero or from Result bit one if byte-shift select 1512 is one. The value of DEST bit nine is selected by multiplexer 1559 either from the value of Result bit nine if byte-shift select 1512 is zero or from Result bit seventeen if byte-shift select 1512 is one. DEST bits ten through one hundred and twenty-seven are similarly selected according to the value of byte-shift select 1512.

[0231] In other words, the value of DEST bit h is selected by a multiplexer either from the value of Result bit h if byte-shift select 1512 is zero or from Result bit k if byte-shift select 1512 is one, where k=16*(h MOD 8)+(h DIV 8).

[0232] It will be appreciated that for any packed data of (m*n) bits, a packed shift circuit that can perform a packed shift of n elements by as many as m bit positions can be similarly modified to perform an alignment shift of m packed elements by as many as m element positions, each element positions having n bits. In other words, in one such embodiment of circuit 1501, the value of Source1′ bit i is selected by a multiplexer either from the value of Source1 bit i if byte-shift select 1511 is zero or from Source1 bit j if byte-shift select 1511 is one, where j=n*(i MOD m)+(i DIV m). In a corresponding embodiment of circuit 1502, the value of DEST bit h is selected by a multiplexer either from the value of Result bit h if byte-shift select 1512 is zero or from Result bit k if byte-shift select 1512 is one, where k=m*(h MOD n)+(h DIV n). It will also be appreciated that since an alignment shift is a logical shift (with zero fill) the correction data provided by correction circuit 1491 may be used by circuit 1502 directly as generated if the correction circuit 1491 is enabled to perform the functions of a logical packed shift of n elements by m bit positions.

[0233]FIG. 16 illustrates an alternative embodiment of a Packed Shift circuit which allows for alignment operations and for packed shifting operations on one hundred and twenty-eight bit packed data. The circuit comprises two identical sixty-four bit shifters with a structure similar to that previously described in FIG. 14b. Each barrel shifter 905 comprises circuit 1461, shifter multiplexers (MUXes) 1441, and shift control 1411. The circuit further comprises a circuit 1501 to provide a transposition of Source1 bits one hundred and twenty-seven through zero (Source1′) to the two barrel shifters. In the most significant barrel shifter 905, the most significant circuit 1461 receives Source1′ bits one hundred and twenty-seven through sixty-four from circuit 1501, and produces one hundred and twenty-eight bits as input to the most significant shifter MUXes 1441. In the least significant barrel shifter 905, the least significant circuit 1461 receives Source1′ bits sixty-three through zero from circuit 1501, and produces one hundred and twenty-eight bits as input to the least significant shifter MUXes 1441.

[0234] Shift control 1410 of the both the most significant barrel shifter 905 and the least significant barrel shifter 905 receive a Left Shift signal and Source2 bits five through zero and directs their corresponding shifter MUXes 1441 to perform effective right or left shifts on their respective quadword of Source1.

[0235] The most significant correction circuit 1491 receives data inputs from the most significant barrel shifter 905 and generates correction data in accordance with the shift operation being performed, the Left Shift signal and the value of Source2, producing as output Result bits one hundred and twenty-seven through sixty-four. If the operation being performed is an alignment shift by byte positions, then both correction circuit 1491 are enabled to perform the functions of a packed shift logical word operation. The least significant correction circuit 1491 receives data inputs from the least significant barrel shifter 905 and generates correction data in accordance with the shift operation being performed, the Left Shift signal and the value of Source2, producing as output Result bits sixty-three through zero.

[0236] Circuit 1502 receives Result bits one hundred and twenty-seven through zero from the most significant and the least significant correction circuit 1491, and stores DEST bits one hundred and twenty-seven through zero. If the operation being performed is an alignment shift by byte positions, then each at each bit h of DEST is stored the value of a bit k of Result, where k=16*(h MOD 8)+(h DIV 8). Otherwise, the bit values of Result are stored to DEST without transposition.

[0237] It will be appreciated that the functionality of circuit 1501 and circuit 1461 may be combined as illustrated by circuit 1601, potentially providing for further optimizations. It will also be appreciated that modifications may be made to the embodiments herein disclosed and that a number of alternative embodiments could be used by practitioners, perhaps in combination with or not in combination with one or more sequences of machine executable emulation instructions, without departing from the spirit of the present invention as claimed.

[0238] Although a great deal of detail has been included in the description and figures, the invention is defined by the scope of the claims. Only limitations found in the claims are considered essential to the invention. 

What is claimed is:
 1. A digital processing apparatus comprising: a decoder to receive a control signal and to identify a first packed shift operation indicating a first shift count source if the control signal includes a first instruction encoding of a packed shift control signal format; a storage location to hold a first packed data having a set of data elements; a shifting circuit to shift the first packed data by a first number of positions responsive to the identified first packed shift operation and the indicated shift count source; and a correction circuit to generate a first replacement data for one of the first number of positions, the correction circuit coupled to the shifting circuit to produce a shifted first packed data comprising the first replacement data.
 2. The digital processing apparatus of claim 1 wherein the positions of the first number of positions are bit positions.
 3. The digital processing apparatus of claim 2 wherein the packed shift control signal format comprises three or more bytes, a third byte of the three or more bytes permitting a three-bit source-destination address.
 4. The digital processing apparatus recited in claim 3 wherein the third byte of the three or more bytes is further permitting a three-bit shift count source address to indicate a memory base address;
 5. The digital processing apparatus recited in claim 4 wherein the third byte of the three or more bytes is permitting the three-bit shift count source address to also indicate a memory index address.
 6. The digital processing apparatus recited in claim 3 wherein the third byte of the three or more bytes is further permitting a three-bit operation code extension to indicate that the first packed shift operation is a packed shift immediate operation;
 7. The digital processing apparatus of claim 1 wherein the packed shift control signal format comprises four or more bytes, a fourth byte of the four or more bytes permitting a three-bit source-destination address.
 8. The digital processing apparatus of claim 7 wherein a first byte of the four or more bytes indicates that the storage location addressed by the three-bit source-destination address holds a packed data having 128 bits.
 9. The digital processing apparatus recited in claim 8 wherein the packed shift control signal format comprises a second byte and a third byte in addition to the first byte permitting an operation code to specify a packed shift operation to perform an arithmetic right shift of word elements, doubleword elements or quadword elements from the first packed data.
 10. The digital processing apparatus recited in claim 8 wherein the packed shift control signal format comprises a second byte and a third byte in addition to the first byte permitting an operation code to specify a packed shift operation to perform a logical shift of word elements, doubleword elements or quadword elements from the first packed data.
 11. The digital processing apparatus recited in claim 10 wherein the fourth byte of the five or more bytes is further permitting a three-bit operation code extension to specify a packed shift operation to perform a logical shift of double quadword elements from the first packed data.
 12. The digital processing apparatus recited in claim 7 wherein the fourth byte of the four or more bytes is further permitting a three-bit operation code extension to indicate that the first packed shift operation is a packed shift immediate operation;
 13. The digital processing apparatus recited in claim 12 wherein the fourth byte of the four or more bytes is permitting the three-bit operation code extension to also indicate that the positions of the first number of positions are byte positions.
 14. The digital processing apparatus of claim 12 wherein the packed shift control signal format further comprises a fifth byte, indicated as the shift count source for an immediate shift count.
 15. The digital processing apparatus of claim 13 wherein the first replacement data generated for one of the first number of positions represents a value of zero.
 16. A processor comprising: a storage location to hold a packed data having M times N bits; a decoder to receive a first control signal of a first control signal format and a second control signal of a second control signal format, the decoder to identify a first shift operation, and a first count less than or equal to M corresponding to the first control signal and to identify a second shift operation, and a second count less than or equal to N corresponding to the second control signal; and a functional unit to shift the packed data by the first count of first positions and generate a first replacement data for one of the first positions responsive to the first shift operation being identified, and to shift the packed data by a second count of second positions generate a second replacement data for one of the second positions responsive to the second shift operation being identified, the functional unit further to produce a shifted packed data comprising the first replacement data responsive to the first shift operation being identified and to produce a shifted packed data comprising the second replacement data responsive to the second shift operation being identified.
 17. The processor of claim 16 wherein the second positions are byte positions.
 18. The processor of claim 17 wherein M is sixteen.
 19. The processor of claim 18 wherein the first positions are bit positions.
 20. (New) The processor of claim 17 wherein M is eight.
 21. The processor of claim 16 wherein the second positions are pixel positions.
 22. The processor of claim 16 wherein the second positions are voxel positions.
 23. An apparatus comprising: a first storage area to store packed data, the first storage area representing a register in a first set of architectural registers; a decoder to decode control signals of a first set of control signal formats; shifting logic to shift a first plurality of packed data stored in the first storage area by a number of shift positions responsive to the decoding of a control signal of the first set of control signal formats; and correction logic to generate a first replacement data for one of the number of shift positions, the correction logic operatively coupled to the shifting logic to produce a shifted packed data comprising the first replacement data responsive to the decoding of the control signal of the first set of control signal formats.
 24. The apparatus of claim 23, wherein the correction logic comprises an integrated circuit.
 25. The apparatus of claim 23, wherein the correction logic comprises a combination of an integrated circuit and a sequence of machine executable emulation instructions.
 26. The apparatus of claim 25, wherein the first set of control signal formats comprise Intel-Architecture control signal formats having three or more bytes, a first byte and a second byte of the three bytes permitting an operation code to specify a shift operation of a packed data format.
 27. The apparatus of claim 26, wherein the first set of control signal formats is permitting a three-bit operation code extension to indicate that the positions of the number of shift positions are byte positions.
 28. A digital processing apparatus comprising: first means for decoding a packed shift operation from a control signal having a packed shift instruction format; second means for shifting a set of data elements by a number of shift positions responsive to the packed shift operation; and third means for generating a first replacement position for a first source data element of the set of data elements, the second means coupled to the first means for producing a shifted first destination data element corresponding to the first source data element of the set of data elements, the shifted first destination data element comprising the first replacement position.
 29. The apparatus of claim 28, wherein the packed shift instruction format is permitting an operation code extension to indicate that the positions of the number of shift positions are byte positions.
 30. A computer system comprising: a memory to store a shift instruction for shifting a packed data by a number of shift positions, the shift instruction having an Intel-Architecture format format permitting a first three-bit source address and a three-bit operation code extension to indicate whether the positions of the number of shift positions are byte positions or bit positions; a storage device to store a software installation, the software installation configured to supply the shift instruction to the memory for execution; and a processor enabled to receive and decode the shift instruction from the memory, the processor including: a first storage location corresponding to the first three-bit source address to store a first packed data, shift logic to shift the first packed data stored in the first storage area by a number of shift positions responsive to the decoding of the shift instruction, and correction logic to generate a first replacement data for one of the number of shift positions, the correction logic operatively coupled to the shifting logic to produce a shifted packed data comprising the first replacement data responsive to the decoding of the shift instruction.
 31. The computer system of claim 30, wherein the correction logic comprises an integrated circuit.
 32. The computer system of claim 30, wherein the correction logic comprises a combination of an integrated circuit and a sequence of machine executable emulation instructions. 